1 Corinthians 15:29 is one of the more enigmatic verses in the Bible. Scholars have long struggled with the meaning of Paul’s questions: “. . . 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?” Just what was going on at Corinth that involved baptism for the dead? Is this literal (water) baptism or something else? Who are the dead – believers or unbelievers? Does baptism help dead unbelievers in the afterlife? If not, what’s the benefit? How does this verse fit the wider context of Paul’s discourse on the resurrection?
James E. Patrick, "Living Rewards for Dead Apostles: ‘Baptised for the Dead’ in 1 Corinthians 15.29," New Test. Stud. 52 (2006): 71–85