Why did he convert to Christianity? He's holding his faith in absolute vain, in my humble opinion, if he believes his god is omniscient as it says in the bible. He might not have tried the blasphemy challenge or said it out loud but the fact that he was an Atheist means that he had had his doubt in the existence of the holy spirit and that one single factor gives his god a plausible reason to send Kirk to hell. So, if he thinks he's smart enough to fool his god to think that his at least subconscious denial in the existence of holy spirit, his god, I believe, should be pretty stupid and not quite omniscient as the bible says and a lot of Christians believe him to be. So, ironically, Kirk's faith in god, the guy floating around up there, is rather insulting to god, which shows the absolute nonsense the religion bears.