In the 1986 musical The Phantom of the Opera by Andrew Lloyd Webber, the Phantom seems to frequently refer to both himself and Christina as "Angel of Music". For example, in "The Mirror/Angel of Music (Reprise)", where the Phantom sings,
I am your Angel of Music
Come to me: Angel of Music
And again in "Phantom of the Opera" he sings,
Sing for me
Sing, my Angel of Music!
Sing for me!
Why does he refer to both himself and Christina as "Angel of Music"? What's the significance behind this?