Peter didn't lie...which means Mormon understanding is incorrect.
So, let me post 1Peter 4:5-6,, here again: "Who shall give account to home that is ready to judge the quick and the dead. For this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit." Pretty clear for anyone to understand. Even a Catholic. Let's support this fact that the gospel is being preached to those in spirit prison that did not have the opportunity to hear and learn of the gospel of Jesus Christ when they were living on earth. 1 Peter 3:18-20, "For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit:
By which also he went and preached unto the spirits in prison; Which sometimes were disobedient, when once longsuffering of God waited in the days of Noah, while the ark was preparing, wherein few, that is, eight souls were saved by water."
So, it's very clear to anyone with any cognitive ability to understand that when the body dies, the spirit we have joined to us does not. It goes to a spirit prison. We know there is a paradise and now we know there is a place for the unrepentant that were not baptized on the ark. Catholics call it purgatory. My feeling is this is hell. But, this is definitely where preaching is going on for those who died without the opportunity to accept the gospel of Jesus Christ.
Still, the only way to enter the Kingdom of God is through baptism of water and the spirit. Paul, who often was at odds with Peter, did agree with Peter about the preaching to the spirits of the dead and understood why the people were doing baptisms for the dead. The Corinthians were having some bad doctrine entering into them and were doubting the resurrection and afterlife. But, they were still baptizing for the dead. And, Paul asked them a simple question, 1Cor.15:29, "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?"
So, explain why this understanding is incorrect. It's very simple English.