The meaning of this custom is uncertain. It is only referred to once in the New Testament (1 Corinthians 15:29). Many interpretations have been offered for this verse. The important questions are the nature of the practice of baptism for the dead and whether or not the apostle Paul approved of it.
Most interpretations of the phrase baptism for the dead fall into one of three categories.
1. Some see it as a metaphor. In Mark 10:38 and Luke 12:50, baptism is used as a metaphor for suffering or martyrdom. Some scholars, interpreting baptism for the dead as a metaphor for martyrdom, would translate it being baptized with a view to death.
2. Many prefer to read the phrase in the normal sense of being baptized on ones own behalf.
3. Martin Luther thought it referred to the practice of baptizing over the tombs of the dead.
4. John Calvin believed it had to do with Christians who called for baptism because they were in danger of dying.
5. Others think it referred to converts who were baptized because of the testimony of Christian martyrs or departed loved ones.
6. The most natural meaning of the words points to a practice of baptism by proxy (acting on behalf of someone else). The phrase seems to indicate that certain people in Corinth would have themselves baptized as a substitute for dead people. The Corinthians may have had a magical view of baptism. That might explain why, to them, Paul belittled his ministry as a baptizer (1 Corinthians 1:14-17). Paul compared the Corinthians experience with that of Israel in the wilderness (1 Corinthians 10:1-13). He described crossing the Red Sea and gathering manna in terms clearly suggesting baptism and the Lords Supper. Paul reminded his readers that neither of those dramatic experiences prevented the Israelites from falling into sin. Perhaps the Corinthians regarded the Christian sacraments as rites that guaranteed their salvation. If so, those who practiced baptism by proxy probably believed that the rite had some benefit for the departed.
Did Paul approve of the practice of baptism for the dead? Probably not. In the particular arguments for the resurrection of the dead in 1 Corinthians 15:29-34, Paul separated himself from the practitioners of such baptism. He didnt imply approval of the practice. Instead, Paul used baptism merely to illustrate his argument. Unless some Corinthians believed in the actual resurrection of the dead, their practice of baptizing on behalf of the dead would obviously be meaningless.