In no passage of the holy canonical books there can be found either divine precept or permission to take away our own life, whether for the sake of entering on the enjoyment of immortality, or of shunning, or ridding ourselves of anything whatever. Nay, the law, rightly interpreted, even prohibits suicide, where it says, 'Thou shalt not kill.' This is proved especially by the omission of the words "thy neighbor," which are inserted when false witness is forbidden.
Saint AugustineAngels are spirits, but it is not because they are spirits that they are angels. They become angels when they are sent. For the name angel refers to their office, not their nature. You ask the name of this nature, it is spirit; you ask its office, it is that of an Angel, which is a messenger.
Saint Augustine