The Encyclopedia Americana (1920)/Baptism for the Dead
BAPTISM FOR THE DEAD, a custom mentioned by Saint Paul in 1 Cor. xv, 29. It probably consisted in the vicarious baptism of a living Christian for a catechumen who had died unbaptized, the latter being thereby accounted as baptized. It is doubtful if the custom was ever widely prevalent, and it seems to have soon died out in the Church, although kept alive by Marcionites and other heretics. It was forbidden by the Synod of Hippo (393). It is observed by the Mormons at the present day.