Canto is a choir director and voice teacher of Heaven, who instructs other angels about how to sing properly. Singing in a choir is an important social outlet for angels, and the beautiful songs of angels can also inspire mortals or even help angels to ward off demons (since the sound is painful for demons). Therefore, singing is a very important skill for angels, so Canto's teachings are in high demand. He's an excellent teacher particularly because he can 'try on' the voices of others to figure out how their own voices work, then teach them how to use it themselves.