Baptism for the Dead

“Otherwise, what will those do who are baptized for the dead? If the dead are not raised at all, why then are they baptized for them?” (1 Corinthians 15:29).

This verse is one of the most difficult in all of Scripture, and has many legitimate possible interpretations; it has also, however, been used to support many strange and heretical ideas. The careful and honest interpreter may survey the several dozen interpretations offered and still not be dogmatic about what it means. But we can be dogmatic, from the clear teaching of other parts of Scripture, about some of the things it does not mean. As to what this verse does mean, we can only guess, since history has locked it into obscurity. . . .

http://www.macarthurcommentaries.com