Those who believe this use the following verse for their proof: “Otherwise, what will they do who are baptized for the dead, if the dead do not rise at all? Why then are they baptized for the dead?” (1 Cor. 15:29).
The practice of vicarious baptism such as that which is practiced by some cults today appeared as early as the second century. It should be noted that a biblical doctrine should not be built on any verse as obscure as this one in 1 Corinthians. Since the Bible clearly teaches that baptism does not save an individual, then being baptized in the place of those who are already dead cannot benefit anyone. The interpretation of this difficult verse yields to an understanding of the Greek preposition hyper. Usually the word means “over” or “instead of.” But there are times when the only translation possible is “concerning.” The translation should be “concerning the dead.” The idea is that Christian baptism concerning death and the promise of resurrection is a meaningless ordinance unless the resurrection is a reality. Paul was questioning why they were continuing to baptize new converts if there was no resurrection, since baptism symbolizes our death and resurrection.
A second interpretation of the passage is that the expression is to be taken synonymously with the meaning found in verse 30, thus being rendered “baptized with reference to the dead.” This would be a nonsacerdotal use of the term “baptism.” That is, the people of whom Paul was speaking were being literally immersed in such severe persecution that they were dying for their faith.
Elmer Towns, Bible Answers for Almost All Your Questions (Nashville: Thomas Nelson, 2003).