Hey,
So basically, this song is played on 2 keys, G Major (or 
Em) and C Major (Am).
The song *only* uses the chords of both keys, (1st 
chord, 4th and 5th), using both major and minor 
chords.

so in the beginning, there is Am (E Minor's 4th chord), 
then goes Em (1st chord, the tonic) then we have G 
which is G Major's tonic, then D, G Major's 5th chord.
then C Major's and A Minor's chords are used in the 
"These open doors" parts.

And *ALL* chords in the song are getting repeated, 
there are only 8 chords used in this song (or less, I'm 
too lazy to count), in all 
instruments, they are just in different octaves and some 
are in different inversions 
6, there are 6 chords, I just counted them.

As you can see, there is no Guitar in this song, so for 
our fellow guitarists, I made a channel to play chords 
along the song, it's "Muted" so click on the red "M" 
button next to the channel name.

And as always, there are few things noted in the song, 
and if you have anything to add, any 
corrections, questions, 
please feel free to comment, and also vote, yes, that 
would be great, voting is good.

Ram.