What in the Chapel is important?

Hint 1 of 7:

On your first visit to the chapel, take a good look around.

Hint 2 of 7:

Find the organ to the right side of the altar in an alcove.

Hint 3 of 7:

Pick up the note from the keyboard.

Hint 4 of 7:

Notice that the organ is missing a part.

Hint 5 of 7:

Enter the confessional and look through the keyhole.