§506
Creed › … › Paragraph 2. "Conceived by the Power of the Holy Spirit and Born of the Virgin Mary"
Mary's virginal motherhood in God's plan
Mary is a virgin because her virginity is the sign of her faith "unadulterated by any doubt", and of her undivided gift of herself to God's will. It is her faith that enables her to become the mother of the Saviour: "Mary is more blessed because she embraces faith in Christ than because she conceives the flesh of Christ."
Source: Catechism of the Catholic Church (Vatican.va)