Mormon scholar, John A. Tvedtnes says: “Baptism for the dead was performed by the dominant church until forbidden by the sixth canon of the Council of Carthage (397). Some of the smaller sects, however, continued the practice.”
Code of Canons of the African Church as canon 18, reads: “It also seemed good that the Eucharist should not be given to the bodies of the dead. For it is written: ‘Take, Eat’, but the bodies of the dead can neither ‘take’ nor ‘eat’. Nor let the ignorance of the presbyters baptize those who are dead.”
Tertullian attributes the practice of 1 Corinthians “baptised for the dead” to the Marcionites.
Epiphanius of Salamis (between 310–320 – 403) reported that he had heard it said that, among followers of Cerinthus, if one of them died before baptism, another was baptized in that person’s name:
For their school reached its height in this country, I mean Asia, and in Galatia as well. And in these countries I also heard of a tradition which said that when some of their people died too soon, without baptism, others would be baptized for them in their names, so that they would not be punished for rising unbaptized at the resurrection and become the subjects of the authority that made the world.
John Chrysostom (c. 347–407) mockingly attributes to the Marcionites of the late 4th century a similar practice: if one of their followers who was being prepared for baptism died before receiving baptism, the dead person’s corpse was addressed with the question whether he wished to be baptized, whereupon another answered affirmatively and was baptized for the dead person.
An interesting example of the views of a prominent non-LDS scholar is related by R.L. Anderson in Understanding Paul, Deseret Book, SLC, Utah, 1983, p. 413. It’s a transcript of a conversation with Dr. Edgar J. Goodspeed, an authority on the New Testament and early Christian documents:
Interview between Dr. Edgar J. Goodspeed and Paul R. Cheesman, held in Dr. Goodspeed’s office on the campus to the University of California at Los Angeles during the summer of 1945.Cheesman: Is the scripture found in 1 Corinthians 15:29 translated properly as found in the King James Translation?
Goodspeed: Basically, yes.
Cheesman: Do you believe that baptism for the dead was practiced in Paul’s time?
Goodspeed: Definitely, yes.
Cheesman: Does the church to which you belong practice it today?
Cheesman: Do you think it should be practiced today?
Goodspeed: This is the reason why we do not practice it today. We do not know enough about it. If we did, we would practice it.
Cheesman: May I quote you as a result of this interview?
Other religions pray for the dead, and some even offer food to the dead. We baptize proxies for the dead.
Unique perspective of a non-Mormon who had been Dean at Harvard Divinity School: