I REMEMBER MARCEL DUPRE

...

While we were still talking, he asked abruptly: « Do you know this choral? » And he played: « Ach Herr, Lass dein Lieb Engelein » (Alas, Lord, leave your dear cherubs) a choral from the Passion according to St JOHN. I said yes and he retorted: « Listen to what can be made out of it. » And he started improvising some variations and a fugue on that choral. At first he played like BACH, then, gradually, found his own style.

...