what is Salieri's prayer

From the text:

"Lord, make me a great composer. Let me celebrate Your glory through music and be celebrated myself. Make me famous through the world, dear God. Make me immortal. After I die, let people speak my name forever with love for what I wrote. In return, I will give You my chastity, my industry, my deepest humility, every hour of my life. Amen".

what was salier's position at the court in vienna