1 Corinthians 15:29

What does the phrase "those who are baptized for the dead" mean in 1 Corinthians 15:29 (NIV)?  I wish I could tell you! Several factors make it difficult to interpret this text. First, the text is very brief and Paul doesn’t elaborate; second, there’s no other reference to this practice in the rest of the New Testament; and third, it seems to suggest what is incompatible with what Paul says about baptism elsewhere.