1 cor. 15

Makes me think of the Mormons, who do believe in Baptising for dead relatives, and hence their desire for accurate genealogies!

Found this in a Christadelphian:

‎What is the baptism for the dead?—(1 Cor. 15:29.)—Q.
‎Answer.—A correspondent says: “A book I have just seen explains this in the light of the fact that there was in the first century an heretical class of people who were baptized on behalf of their dead friends. This seems to fit the matter better than either the ‘elliptical’ or the baptism into Christ’s death. The Greek (nper) also means on behalf.”
‎This may “fit the matter,” but we suspect the fitting is the other way about; that is, the existence of pro-mortem baptists has been invented to explain the apostolic phrase. It is by no means clear that such a class ever existed. The tradition that there were such people, goes back, of course, a long way; but that might easily be traced to the apostle’s words themselves, as giving rise to the idea that there were such people. It is very improbable, even if there were such people, that Paul would virtually endorse their absurd practice by making it an argument for the resurrection. It could not prove the resurrection, but only that such baptisers expected it, which would be rather a weak fact for a logician like Paul to employ. It seems far more reasonable to assume that Paul’s allusion is to something true in itself and recognised by the Corinthians to whom he was writing. Both these features are to be found in baptism. It has to do with death, the dead, and the burial of the dead. It is “a likeness of the death of Christ.”—(Rom. 6:6.) The dead (to sin) are the subjects of it (Rom. 6:2), and it is a burial of such in Christ.—(Col. 2:12.) These things were received by the Corinthians; and Paul might as well ask “if there is no resurrection of the dead, what is the meaning of all this? Do men go through this death-performance for the sake of rejoicing over the curse, or is it not that there is a hope of rising again to which all this points?”

. Vol. 10: The Christadelphian: Volume 10. 2001 (electronic ed.) (331–332). Birmingham: Christadelphian Magazine & Publishing Association.