In Amulek's testimony concerning the effects of the Atonement, he states, "do not procrastinate the day of your repentance until the end; for after this day of life, which is given us to prepare for eternity, behold, if we do not improve our time while in this life, then cometh the night of darkness wherein there can be no labor performed." Critics of the Book of Mormon assert that passages in the Book of Mormon such as Alma 34:32-34; Mosiah 15:26; and Moroni 8:22-23 forbid the modern LDS practice of baptism for the dead.
However, according to Matt Roper, the first two passages are concerned with those people who "willfully rebel" against God after having had the opportunity to repent and receive the Gospel, and have nothing to do with proxy baptism for those denied an opportunity. Moroni 8:22-23 does not forbid baptism for the dead either, but merely says that those who die without the law are not under condemnation until they can receive the law. Someday all men will hear the gospel and have the chance to repent and receive any blessings which baptism offers, but they can't repent until they are taught.
As for biblical support for the practice of baptism for the dead, LDS students of the scriptures usually turn to 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? Concerning this verse, Roper notes that although critics might contend that 1 Corinthians 15:29 has absolutely nothing to do with proxy baptism, most biblical scholars today admit that this is exactly what Paul had reference to, although most will say that they don't know much about it. The Lutheran scholar and bishop Krister Stendahl states that "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." "The normal reading of the text," writes Gordon Fee, "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." It seems that in Corinth," writes Raymond E. Brown, "some Christians would undergo baptism in the name of the deceased non-Christian relatives and friends, hoping this vicarious baptisms might assure them a share in the redemption of Christ." [Matthew Roper, Review of Weldon Langfield, The Truth about Mormonism: A Former Adherent Analyzes the LDS Faith. Bakersfield: Weldon Langfield Publications, 1991; 124 pp., in Review of books on the Book of Mormon, Vol. 4, F.A.R.M.S., 1992, pp. 83-84]