I learned a lot from my studies and I present the following andd let each person decide for himself (or herself)

In  1 Cor. 15, Paul reminded the Corinthians that he had taught them categorically, as a first and foremost component of his good news, how Christ "died for our sins" but had been "raised to life again on the thirdday",.

 

He listed the witnesses who had seen him, "most of whom are still living." He reminded them that he to witness to the Risen Christ, how meeting Christ  had revolutionized Paul, so that "I worked harder than any of them, though it was not I but the grace of God which is with me" If he and the other witnesses were proclaiming Christ as risen from the dead, "how can some of you say that there is no resurrection of the dead, then Christ? But if there is no resurrection of the dead, then Christ has not been raised."

If Christ had never , in precise historic fact, risen from the dead then Paul's preaching and Corinthians faith and actions were for nothing:' You are still in your sins" On the other hand if no dead are ever raised Paul had willfully misrepresented God and his Son had committed perjury by swearing that Christ had risen. "But Christ has raised from the dead!" Paul   countiues "And he makes certain that others will also be raised to life because of Christ". Paul, then in 1 Corinthians 15:29 refers to an early practice of vicarious
baptism for the dead.

 

While explaining that without the resurrection of Christ and of all mankind, faith and repentance and even his own preaching would be in vain, he asks "Else what shall they do which are baptized for the dead?' What does this mean? Some Christians Pastors I have discussed this with thought that Paul mentions this custom almost in passing, using it in his arguments substantiating the resurrection of the dead, but without necessarily approving the practice (this is a very common explanation). But why would Paul use some heretical practice in his arguments for the resurrection? In my studies of Paul there is NO WAY he would stand for it!

This is the same Apostle who went to great lengths to correct wrong teachings. And if he mentioned it in passing, wouldn't that mean that his listeners, the Corinthians, were fully familiar with the practice and its
ramifications?

Many Commentators have long recognized that the plain meaning of the passage is that living people were being baptized for dead friends or relatives, but they usually try to get out of it by placing some other, more dubious interpretation on this verse. Thus Henry Halley: (Halley's Bible Handbook, p. 600.)
 

This seems to mean vicarious baptism, that is, baptism for a dead friend. But there is no other Bible reference to such a practice, and no evidence that it existed in the Apostolic Church. Perhaps a better translation would be "baptized in hope of the resurrection. But Paul's statement itself is evidence that baptism for the dead existed in the Apostolic Church! The NIV Study Bible admits that, "The present tense
suggests that at Corinth people were currently being baptized for the dead." And if "baptized for the dead" really means "baptized in hope of the resurrection", it is expression translators have no knowledge of, or they would have used it to avoid the apparent meaning of the passage.

What does the evidence show?
1) It was practiced
2) Paul was aware of the practice and did not clearly condemn it as heretical

 

 

It appears to me that the early church practiced an ordinance known as baptism for the dead. As I consider my own historical knowledge of the early church limited, let me refer you to the writings of Dr. Hugh Nibley's.  Mormonism & Early Christianity

 

Christ Preached to the Dead

 

Following 1 Peter 4:6, it was believed in the early church that Christ preached "to them that are dead." "For this reason," says the Lord in the "Discourse to the Apostles," "have I gone below and spoken to Abraham, Isaac, and Jacob, to your fathers, the prophets, and preached to them, that they might enjoy their rest in heaven."  To quote more fully a passage already cited from the Epistle of Barnabas, "He opens to us, who were enslaved by death, the doors of the temple, that is the mouth; and by giving us repentance introduced us into the . . . spiritual temple builded for the Lord."  Christ is the king "of those beneath the earth," says Hippolytus, "since he also was reckoned among the dead, while he was preaching the gospel to the spirits of the saints [or holy or righteous ones]." The same writer says Jesus "became the evangelist of the dead, the liberator of spirits and the resurrection of those who had died."   The idea is thus expressed by the author of the Sibylline Discourses: "He will come to Hades with tidings of hope to all the saints, and [tidings] of the end of time and the last day."  Clement of Alexandria is thus following the accepted doctrine when he says: "Christ went down to Hades for no other purpose than to preach the gospel."

 

A great favorite with the early Christians was a passage from the apocryphal  Book of Sirach: "I shall go through all the regions deep beneath the earth, and I shall visit all those who sleep, and I shall enlighten all those who hope on the Lord; I shall let my teaching shine forth as a guiding light and cause it to shine afar off." Schmidt distrusts the claims that this was a genuine Hebrew scripture, since it is found only in Christian translations;  but for our purpose that fact only enhances its value. Whatever its source, the ancient church received it gladly, as it did another Jewish text attributed to Jeremiah and quoted by Justin and (no less than five times) by Irenaeus: "The Lord God hath remembered his dead among those of Israel who have been laid in the place of burial, and has gone down to announce to them the tidings of his salvation."  The Christians angrily accused the Jews of having expunged this passage from their scripture in order to damage the Christian cause, from which it would appear that the doctrine of salvation for the dead was a major issue in those early times, and a most precious possession of the church. 

 

In all these texts we are told that Jesus did not simply "harrow" hell and empty it with a single clap of thunder, as was later imagined. The whole emphasis in the Descensus was on the Kerygma, or the Lord's preaching of the gospel.  He preached the gospel in the spirit world exactly as he had done in this one. Our informants insist, in fact, that Christ's mission below was simply a continuation of his earthly mission, which it resembles in detail. The spirits there join his church exactly like their mortal descendants, and by the same ordinances.

 

"Descending into the other world," says the old hymn, Christ "prepared a road, and led in his footsteps all those whom he shall ransom, leading them into his flock, there to become indistinguishably mingled with the rest of his sheep." "I made a congregation of the living in the realm of the dead," says the Lord in the Odes of Solomon, "I spake to them with living lips . . . and sealed my name upon their heads, because they are free and belong to me." Another Ode says: "I went to all my imprisoned ones to free them . . . and they gathered themselves together to me and were rescued; because they were members of me and I was their head."  "He went down alone," writes Eusebius, citing a popular formula, "but mounted up again with a great host towards the Father."  Tertullian is more specific: "Christ . . . did not ascend to the higher heavens until he had descended to the lower regions [lit. lower parts of the worlds], there to make the patriarchs and prophets his compotes."  The word compos [singular form] in Tertullian always denotes "one who shares secret knowledge;"  he made them his disciples in the other world.

 

 

 

Though  rejected at his first coming, says Irenaeus, Christ nonetheless "gathers together his dispersed sons from the ends of the earth into the Father's sheepfold, mindful likewise of his dead ones who fell asleep before him; to them also he descends that he may awaken and save them." 106 The philosopher Celsus, making fun of the strange doctrine, asks Origen: "Don't you people actually tell about him, that when he had failed to convert the people on this earth he went down to the underworld to try to convert the people down there?" It is significant that Origen answers the question, for all its mocking tone, in the affirmative: "We assert that Jesus not only converted no small  number of persons while he was in the body . . . but also, that when he became a spirit, without the covering of the body, he dwelt among those spirits which were without bodily covering, converting such of them as were willing to Himself." 107 According to this the dead not only have the gospel preached to them, but are free to accept or reject it, exactly like the living.
(Mormonism & Early Christianity : 4 : 121 : 1 - : 4 : 122 : 1 )

 

How the Dead Received Baptism

John's function in the spirit world, like the Savior's, was identical with his mission on this earth. Yet his very special mission here was to baptize. Likewise the worldly preaching of the Lord and the apostles was to prepare their hearers for baptism. It is not surprising then to read in the Pastor of Hermas, one of the most trustworthy guides to the established beliefs of the early church, that not only Christ and John but also "these Apostles, and the teachers who had proclaimed the name of the Son of God, after they had fallen asleep in [the] power and faith of the Son of God preached likewise to the dead; and they gave them the seal of the preaching. They accordingly went down with them into the water and came out again. But although they went down while they were alive and came up alive, those who had fallen asleep before them (prokekoimemenoi) went down dead, but came out again living; for it was through these that they were made alive, and learned the name of the Son of God."  The Latin version reads: "These Apostles and teachers who had preached the name of the Son of God, when they died in possession of his faith and power, preached to those who had died before, and themselves gave them this seal. Hence [igitur] they went down into the water with them; but they who had died before went down dead, of course, but ascended living, since it was through them that they received life and knew the Son of God."

Needless to say, this text has caused a great deal of embarrassment to interpreters, ancient and modern. The source of the trouble is obvious: there are two classes of living persons referred to, those who enjoy eternal life, and those who have not yet died on this earth. The apostles (or whoever "they" were) belonged to the latter class when they went down living to be baptized for those who had gone before; a sharp contrast is made between their state--they being alive both before and after the ordinance--and that of those who were actually dead and yet received eternal life through the ministrations of baptism. What is perfectly clear is that the apostles while they were still living performed an ordinance--the earthly ordinance of baptism in water--which concerned the welfare of those who had already died. That it was an earthly baptism which could only be performed with water is emphatically stated in the sentences immediately preceding those cited: "It is necessary, he said, for them to come up through the water in order to be made alive; for otherwise none can enter the Kingdom of God . . . therefore even the dead receive the seal. . . . The seal is of course, the water."

 

 

 

 A place a person verify such a practice ever existed is from  non-LDS sources . Read the following:
(Sorry for spelling errors these are from my notes and files)

It will be seen that even those scholars who opine that Paul disapproved of proxy baptism acknowledge that he was citing the practice as part of his defense of the resurrection.

 

 Harper's Bible Commentary:
The first two rhetorical questions [asked by Paul in vs. 29] refer to thepractice of the Corinthians to undergo baptism vicariously for their dead inthe hope of saving them. More than thirty interpretations have been proposed to explain this practice, but none is satisfactory. Paul does not questionthe merits of it but refers to it to elucidate his point. (Harper's Bible
Commentary, San Francisco, California: Harper & Row, Publishers, 1988, p.
1187)

The Abingdon Bible Commentary:
Paraphrase: "We can scarcely bring ourselves to imagine what is involved indenying the resurrection. Even some who deny the doctrine prove that they
really believe it by their otherwise meaningless custom of undergoingvicarious baptism for their relatives who have died before being received by baptism into the Christian fellowship. . . ."

The interpretation followed above presupposes a local usage--namely, baptism in behalf of the dead--which Paul neither commends nor condemns. . . . (The
Abingdon Bible Commentary, Garden City, New York: Doubleday & Company, Inc.,
1957, reprint, p. 1192)

One Volume Commentary on the Bible:

St. Paul then, almost in parenthesis, touches on what appears to have been acustom  among the Corinthian Christians of baptizing by proxy on behalf ofsome, presumably members of the same family, who had died unbaptized and
might therefore, it was thought, miss their chance of being incorporatedinto the fulness of Christ's Kingdom at his Advent. This practice, says theapostle, makes as little sense as his own daily contempt for physical death,if there is no resurrection. (William Neil, One Volume Commentary On The
Bible, London: Hodder and Stoughton, 1973, p. 461)

The Interpreter's One-Volume Commentary on the Bible:
After sketching briefly the drama of the end, Paul resumes his attack onthose denying the possibility of man's resurrection. Scribes andcommentators have sought to avoid translating vs. 29 as in the RSV, since it
is difficult to think that Paul would approve of baptism by proxy. But atthis place he is throwing up questions to expose the illogical nature of the
beliefs and practices of those denying the resurrection, and he withholds
his personal judgment of baptism on behalf of the dead. (The Interpreter's
One-Volume Commentary on the Bible, Nashville: The Abingdon Press, 1971, p.
811)

Leon Morris, The First Epistle of Paul to the Corinthians:
. . . the most natural meaning of the expression [used by Paul in 1 Cor.
15:29] is that some early believers got themselves baptized on behalf of
friends of theirs who had died without receiving that sacrament. (Leon
Morris, The First Epistle of Paul to the Corinthians, London: Tyndale Press,
1964, p. 218)

 

 

The New Century Bible Commentary:
The prima facie meaning of these words [in 1 Cor. 15:29] points to a
practice of baptism by proxy. (F. F. Bruce, The New Century Bible
Commentary: 1 and 2 Corinthians, Grand Rapids, Michigan: Eerdmans Publishing
Co., 1971, p. 337)

James Moulten and George Milligan, The Vocabulary of the Greek New
Testament:
Close inspection of the language of the reference makes all attempts to
soften or eliminate its literal meaning unsuccessful. An endeavor to
understand the dead as persons who are "dead in sin" does not really help;
for the condition offered, if the dead are not being raised at all, makes it
clear that the apostle is writing about persons who are physically dead. It
appears that under the pressure of concern for the eternal destiny of dead
relatives or friends some people in the church were undergoing baptism on
their behalf in the belief that this would enable the dead to receive the
benefits of Christ's salvation. (James Moulten and George Milligan, The
Vocabulary of the Greek New Testament, Grand Rapids, Michigan: Eerdmans
Publishing Co., 1981, p. 651, original emphasis)

Gerhard Kittel and Gerhard Friedrich, Theological Dictionary of the New
Testament:
None of the attempts to escape the theory of a vicarious baptism in
primitive Christianity [as indicated in 1 Cor. 15:29] seems to be wholly
successful. (Harald Riesenfeld, "Hyper" ["huper"], in Gerhard Kittel and
Gerhard Friedrich, editors, Theological Dictionary of the New Testament,
Grand Rapids: Michigan: Eerdmans Publishing Co., 1974, vol. 8, pp. 512-513)

Krister Stendahl, "Baptism for the Dead: Ancient Sources, in Encyclopedia of
Mormonism:
. . . the text [1 Cor. 15:29] seems to speak plainly enough about a practice
within the Church of vicarious baptism for the dead. (Krister Stendahl,
"Baptism for the Dead: Ancient Sources," in Daniel Ludlow, editor,
Encyclopedia of Mormonism, New York: MacMillan, 1994, vol. 1, p. 97)

The Expositer's Bible Commentary:
Here Paul returns to his argument for the resurrection of the dead. There is
a special difficulty in understanding v. 29 because we do not know the
background of the words "baptized for the dead." There are many
interpretations, but it is difficult to find a satisfactory one. The present
tense "baptize" suggests that the practice of baptizing for the dead was
current and evidently well known to the Corinthians. . . .
. . . its ["huper's", the Greek word behind "for" in "baptized for the
dead"] basic meaning with the genitive is "for," "in behalf of," or "in the
place of."
According to [H. A. W.] Meyer, this verse means that believers already
baptized were rebaptized for the benefit of believers who had died
unbaptized. This was done on the assumption that it would count for the
unbaptized dead and thereby assure their resurrection along with the
baptized, living believers. . . .

At any rate, Paul simply mentions the superstitious custom without approving
it and uses it to fortify his argument that there is a resurrection from the
dead. (The Expositor's Bible Commentary, Grand Rapids, Michigan: Zondervan
Publishing House, 1976, vol. 10, pp. 287-288)

The Interpreter's Dictionary of the Bible:
. . . [to judge from 1 Cor. 15:29, certain Christians] would seem to have
undergone the rite [proxy baptism] for the benefit of departed relatives.
(The Interpreter's Dictionary of the Bible, Nashville: The Abingdon Press,
1962, vol. 1, p. 350)

 

The Interpreter's Bible:
. . . whatever doubt some members of the Church had concerning it, there
were others who were such firm believers in the resurrection that they
submitted to this rite of vicarious baptism on behalf of certain of their
brethren, probably catechumens, who had passed away before they had been
baptized and received into full membership of the Church. (The Interpreter's
Bible, New York: The Abingdon Press, 1952-1957, vol. 10, p. 240)

The Jerome Biblical Commentary:
It seems that in Corinth some Christians would undergo baptism in the name
of their deceased non-Christian relatives and friends, hoping that this
vicarious baptism might assure them a share in the redemption of Christ.
Paul sees in this strange practice an implied faith in the resurrection of
the dead. (The Jerome Biblical Commentary, Englewood Cliffs, New Jersey:
Prentice-Hall, Inc., 1968, vol. 2, p. 273)

Gordon Fee, The First Epistle to the Corinthians:
The normal reading of the text [1 Cor. 15:29] is that some Corinthians are
being baptized, apparently vicariously, in behalf of some people who have
already died. It would be fair to add that this reading is such a plain
understanding of the Greek text that no one would ever have imagined the
various alternatives were it not for the difficulties involved. (Gordon Fee,
The First Epistle to the Corinthians, Grand Rapids, Michigan: Eerdmans
Publishing Co., 1989, pp. 763-764, emphasis added)

And finally , I have found reading different  translations and noted private translations of 1 Cor. 15:29 can

Help me get a clearer view.

The Confraternity Version, a major Catholic translation prepared under the
guidance of the Catholic Bishops of the United States:

Else what shall they do who receive baptism for the dead? If the dead do not
rise at all, why then do people receive baptism for them?

The Revised English Bible:
Again, there are those who receive baptism on behalf of the dead. What do
you suppose they are doing? If the dead  are not raised to life at all, what
do they mean by being baptized on their behalf?

The Revised Standard Version:
Otherwise, what do people mean by being baptized on behalf of the dead? If
the dead  are not raised at all, why are people baptized on their behalf?

The New Revised Standard Version, whose translation committee included the
renowned Greek scholar Bruce Metzger:
Otherwise, what will those people do who receive baptism on behalf of the
dead? If the dead  are not raised at all, why are people baptized on their
behalf?

The New Jerusalem Bible:
Otherwise, what are people up to who have themselves baptized on behalf of
the dead? If the dead are not raised at all, what is the point of being
baptized on their behalf?
J. B. Phillips:
. . . being baptized for the dead by proxy.


The New English Bible:
Again, there are those who receive baptism on behalf of the dead. Why should they do this? If the dead  are not raised to life at all, what do they mean by being baptized on their behalf?

The New Revised Translation:
Else what shall they do which are baptized for the dead, if the dead rise
not at all? Why are they baptized for their dead?

Andy Gaus:

Tell me, what are they doing when they hold proxy baptisms on behalf of
departed souls? If the dead  still aren't going to be raised, why have
baptisms for them? (The Unvarnished New Testament: A New Translation from the Original Greek)