Themes on 'Redemption of the Dead' is not only depicted in historical Christian art but it is also found in ancient Christian writings. 'Baptism for the Dead' is just one aspect of this concept of redeeming the dead that was taught by the Early Christian Church.
Christ and the Ressurection
"And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. Then opened he their understanding, that they might understand the scriptures, And said unto them, Thus it is written, and thus it behoved Christ to suffer, and to rise from the dead the third day" (Luke 24:44-46)