They say
Baptism for the dead is a Mormon invention. Hebrews 9:27 closes the door.
1 Corinthians 15:29: Paul proves Easter with a practice his church already had. You do not win an argument with a rite you despise. 1 Peter 4:6: the gospel was preached to the dead. Hebrews 9:27 is a court date, not a locked door. Gospel Topics: Baptism for the Dead. FAIR’s overview is the short stack.
1 Corinthians 15:29
KJV · Else what shall they do which are baptized for the dead, if the dead rise not at all? why are they then baptized for the dead?
NRSVUE · Otherwise, what will those people do who receive baptism on behalf of the dead? If the dead are not raised at all, why are people baptized on their behalf?
1 Peter 4:6
KJV · For for this cause was the gospel preached also to them that are dead.
NRSVUE · For this is the reason the gospel was proclaimed even to the dead.

