Some have wondered how an angel can be called a saint. When we speak of a “saint,” we ordinarily refer to a person whose life reflects, or did reflect, what the Church calls “heroic sanctity” — that is, a life transparent to the mercy and love of Jesus Christ. Down through the ages the lives of many such persons have come to the Church’s attention, and she has recognized them with the title of “saint.”
Half a dozen of St. Paul’s letters are addressed to Christians as “saints.” In this context, the term refers to those individuals’ status as members of Christ’s Mystical Body. We speak of the Communion of Saints to designate the entirety of those who belong to Christ. The term “saint” does apply primarily to human beings, but refers to any being in heaven.
Sacred Scripture singles out and names three great angels: Michael, Gabriel, Raphael. The Church applies the term “saint” to these particular angels because of their great significance in the history of salvation.