I am astonished that you are so quickly deserting the one who called you by the graceof Christ and are turning to a different gospel-which is really no gospel at all. Evidently some people are throwing you into confusion adn are trying to pervert the gospel of Christ. But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned! As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let him be eternally condemned! Galatians 1:6-9
No, it seems to me that Paul has pretty much covered the Mormon doctrine right here, down to the details of how the doctrine might come about (an angel from heaven-Moroni, his father, etc...)
After all, legend has it that after Jesus had been crucified he went to the desert and found the original "Mormon" who he then sent to the Americas. But then, this would be contradictory to Paul's words, and thus contradictory to the Bible, making the Book of Mormon not "another testament" of Christ, but a different one, and thus, exactly what Paul warned us against.
I'm sure Lyric's Dad can rationalize and clarify this for us if he rejoins, although this all seems pretty clear to me.
Let's all keep in mind, though, that when Lyric's Dad left the "church" he likely also left his family, as his wife and children would have turned their backs on him for abandoning the Mormon faith. It is not uncommon for families to fall apart because one of the parents sees through the Mormon shroud and leaves the church, and in so doing their children, who have been raised in the church, and their still-believing spouse, are so confused its as if they don't even know this family member anymore. It's brainwashing at its finest. This may have been the deciding factor in his rejoining the church...if so, Lyric's Dad needs our prayers a lot more than he needs our antagonism.