The Gloria from tonight's Mass.
OK, here is the Credo, too.
As an aside, I have heard some say that Mozart may have been a Freemason (with a nod to the Magic Flute), and he certainly was not portrayed flatteringly in Amadeus. I don't know anything about the state of his soul.
But a man who can make music like this to praise God should get some sins forgiven at least, I would think. In any event, it might be a proper sign of gratitude to pray for his soul.
Eternal rest grant unto him and may perpetual light shine upon him. May his soul rest in peace.