The best part of the episode comes after this, when the groom's family starts thanking Larry on the low and he acts like he did it on purpose to look cool hahahaha.
The song Larry's "singing" is the chorus of the showtune "June is Bustin' Out All Over." ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-EAk28Z4qIKc.html
He can't help but more or less subtly mock Jesus and Christianity. It's all designed to get non-Jews to play into it, because it's so clever and whimsical. Trouble is, you can't out-Jew God. God became a Jew in Jesus Christ. He's Super Jew. Face it: unless you repent sincerely, it's all downhill after you crucify God.
I know that this is the point of this segment (car trip) but...goddamn Larry is annoying lol. That being said, the way he ruins the baptism is hilarious!