At the age of 12, if I remember correctly, he decided to dedicate all his music to the glory of God.
I am certain that's the single reason he is without peer in the world of composers. I have many works by Bach and after collecting as many as I could in some 20 years, I have many more to go. And amazingly there is so little repetition of his themes that one wonders where he came up with his ideas. I have to guess God honored his desire to write for His glory by giving him a deep well from which to draw.
Speculating, I suspect the saints will sing his music in God's presence.
"When Bach had said his piece, he had said it all."