I have always wondered, if Catholicism can be really called monotheistic. I understand that God is one being that exists in three persons, the Father, the Son, and the Holy Spirit. But you must also recognize the all the saints, the prophets, Mary Queen of Heaven, the Archangel, Guardian angels, and normal angels. Isn’t the Catholic Church coming close to being a polytheistic religion?
We recognize that the saints, prophets, the Blessed Virgin Mary, and all the angels are NOT God. That leaves us with God. As Catholics, we believe that there is one God. This means that Catholicism is a monotheistic religion.
See this article from the original Catholic Encyclopedia for more:
Fr. Vincent Serpa, O.P.