"Else what shall they do which are baptised for the dead, if the dead rise not at all? why are then' then baptised for the dead?"
This is perhaps one of the most puzzling things that Paul wrote in his epistles. One explanation that fits in perfectly with Paul' s line of reasoning revolves around the meaning of the word "for." The Greek word is "huper," and the general translation is "in behalf of." But there are exceptions to this meaning. Sometimes the word is used in the sense of "considering" or "in view of."
For example, 2 Thessalonians 1:4 says: "So that we ourselves glory in you in the churches of God for your patience and faith in all your persecutions." Here Paul is saying, We glory in you considering (or in view of) your patience and faith. In Romans 15:9--which reads, "And that the Gentiles might glorify God for his mercy"--it can be translated "considering his mercy."
Please notice now that this same word "huper," which is translated "for," is used both ways in 1 Corinthians 15:29: "Else what shall they do which are baptised for [considering] the dead, if the dead rise not at all? why are they then baptised for [in view of] the dead?"
If we substitute this other meaning of the word "for," the text makes perfect sense. Paul' s whole theme in the chapter is the resurrection--its importance and necessity. He is saying, Why even be baptised if there is no resurrection from the dead? The very meaning of baptism would be nullified. With no resurrection, the entire symbolism of baptism--death, burial, and resurrection--would be reduced to an empty ritual.