It's not exactly just three chords, with the chord on the first "peace" which according to one source is called a "G# Ø half dimº" chord, followed by the suspension on "heav-" aka "G add9 flat5 6th no3" [1].
There are some really cool passing chords in Silent Night.
Re:“Silent Night” turns 200
by ianbicking on Saturday December 15, 2018 @12:11AM
(#18687174)
Talking about a rock and roll structure does go nicely with the image from the article, of the debut of the song by a young priest (himself inspired by peace in the face of war) and his composer friend, accompanied by just a guitar.
One might think this structure is only a recent invention with early blues and rock & roll. Is it unusual for a 200-year-old song to follow this pattern? How old is the three-chord musical structure?