Early Christian memory of vicarious rites and multiple heavens
Paul assumes his Corinthian readers already know a baptism for the dead and does not pause to invent it; he uses it as evidence of the resurrection.
Whatever later commentators wish 1 Corinthians 15:29 meant, the plain sense is vicarious baptism. Jewish and Christian apocalypses also know multiple heavens. D&C 76 and D&C 128 are reading Paul, not hijacking him.

