The key doesn't really matter, use what you know in another key and play it in A by moving up/down however many half or whole steps. I've never played the song, but just from listening briefly here is a little of the basics below. Also the song doesn't stay in A he moves between keys - Dmin from what I listened to (changes key/modes within the song), realize that Richard Smallwood has a classical piano background so a lot of the large chords you may normally use in contemporary gospel you may not need to use and may want to be more conservative with. It would take more time to write out all the changes and keys so here is some of the basics without me going too far into theory and key changes.
Intro
E/
A/E-A-C#
(hold)/F-A-D
(hold)/G-C#-E
A/F-A-D
(hold)/E-A-C#
E/F-A-D
A/E-A-C#
again for intro and also you can invert chords for different approach/feel. You can add filler, but I wouldn't add too much so that you keep the classical feel of the song.
move to Dm coming out of intro
/F
/E
D/F-A-D
...Holy
/D
/C
Bb-G/D-F-Bb
...Holy
/G
/F
C-G-Bb/G-C-E
...Thou Art
/C
/Bb
F/C-E-A
...Holy
/F
/E
Bb-F-A/F-A-D
/Bb
/C
E/G-Bb-D - Ho...
/Bb - ly
A-G/C#-E-G-A - Thou
/C# - Art
w/turnaround in Bass back to Dm
F/F-A-D - God
E/
A/
G/
F#/C-D-F#
E/G#-D-F
A/G-C#-E
back to top of verse
I didn't listen to all of it, but this should get you going on it...
