Paul asked the rhetorical question in 1 Corinthians 15:29,
"Else, what shall they do which are baptized for the dead, if the dead rise not at all? why are they then baptized for the dead"(KJV).
The LDS believe the ancient biblical injunction that all must be baptized to enter into the
The Latter-day Saints do believe, with the Apostle Paul, that, under certain circumstances, living people can be baptized vicariously for those who did not receive this saving ordinance while living and are now deceased. Baptism for the Dead is just one of the ordinances performed vicariously in the LDS Temples. Vicarious means for and behalf of someone else in much of the same way that the Savior's atonement was a vicarious act for the Salvation all of mankind.
Krister Stendahl, a Lutheran bishop, a preeminent theologian the dean of the Harvard School of Theology discusses the practice in ancient times. He states, "the text seems to speak plainly enough about a practice within the Church of vicarious baptism for the dead. This is the view of most contemporary exegetes." ( Krister Stendahl, "Baptism for the Dead," in Daniel H. Ludlow, ed., Encyclopedia of Mormonism, 4 vols. (New York: Macmillan, 1992), 1:97.)In a clip from the LDS documentary 'Between Heaven and Earth,' Bishop Stendahl speaks about the LDS practice of vicariously baptizing those who have died without having received this essential ordinance.
Clement of Rome [30-100 A.D.], hints to this when he wrote: "Thou shalt raise me up, and I shall confess unto Thee;" (Psa.28:7), and again I laid me down, and slept; I awaked, because Thou art with me;" (Compare Psa.3:6), and again, Job says, "Thou shalt raise up this flesh of mine, which has suffered all these things." (Job. 19:25-6).
In the Ethiopic document known as the Testament of Our Lord and Our Savior Jesus Christ 38–39, Jesus tells his apostles, "For this reason I descended and conversed with Abraham, Isaac, and Jacob, with your fathers the prophets, and I announced to them, in Sheol, the rest in the heavens where they shall come. With my right hand, I gave them the baptism of life, pardon and remission of all sin, as I did for you, and (as I shall do) hereafter for those who shall believe in me." He then tells them that he who believes "shall come out of the prison and will be delivered from chains, from punishment and from the fire," to which the apostles respond, "O Lord, you have truly given us joy and rest, for because of their faith and their confidence, you have announced to our fathers and to the prophets; also for us and for all (who believe in you)."