HOW GREAT THOU ART

I love this

I have already bought it

that chords consists of B flat, D, F, A flat (in B flat major scale)

a 7 flat chord is kinda like the IV chord of the IV chord.

Yeah all you are doing in this case is tonicizing the IV chord - so yeah it is basically a IV of IV, but is also the bVII

oh dear iv got to go and uncurl my toes......

Great version of this wonderful hymn!!!

or itunes

a 7 flat chord simply means you take the 7th scale degree of whatver key you are in and lower it a half step (makin it flat) then do a major chord on it...for example in teh key of G, the 7th scale note is F#, lower it a half step to F, play an F major chord...that's it
How Great Thou Art is usually in B flat Major, so the 7flat chord will be A flat...hope this helps.

Thank you for the information, God bless you