it's a cousin of preach
a) "what i said is so true, like a preacher at church"
b) when other's respond to your statement with chuch, it means 'true! we firmly believe/love what you said, like you preachin to us at church! '
Ex.2 All you stupid fucks that don’t know shit and think snoop invented that word are a bunch of faggot-ass losers, CHUCH!
Oh Chuch that shit is the shit.