Question: "What is baptism for the dead?"
Answer: In short, it looks like the baptism of the dead was a non-biblical practice of the Corinthian church where a living person was baptized in lieu of a person that passed away, as a means of making a public profession of faith for a person that was already deceased. We can, essentially, think of it as the practice of baptizing a deceased person.
In context, Paul writes this as an answer to the cityís questions about resurrection. Heís saying, "If you donít believe in life after death, why are you concerned with the dead?" The reference coming up that involves Luke 16:26 answers the Corinthiansí question from another angle. This verse says (indirectly) that our decision for or against Christ is made before we die. According to Luke, we canít change our minds after death. This offers more evidence that the practice of baptism for the dead is a futile concept.
What was being baptized for the dead? It is a mysterious passage, and there have been more than thirty different attempts to interpret it. 1. The plain meaning of the Greek in verse 29 is that some people are being baptized on behalf of those who have died--and if there is no resurrection, why are they doing this? 2. Either Paul is referring to a pagan custom (notice he uses they, not "we"), or to a superstitious and unscriptural practice in the Corinthian church of vicarious baptism for believers who died before being baptized. 3. Either way, he certainly does not approve of the practice; he merely says that if there is no resurrection, why would the custom take place? The Mormon practice of baptism for the dead is neither scriptural or sensible. Baptism for the dead is a practice that was common in the pagan religions of Greece and is still practiced today by some cults; but it doesn't change a person's sentence, for that is determined while he lives (Luke 16:26).