God's Plan for Mary
From the Catechism of the Catholic Church, Simplified
Why Born of a Virgin? (502-504)
The virgin birth highlights Christ's person and his redemptive mission. Mary's virginity shows God's absolute initiative in the Incarnation. Because Jesus has only God as Father, "he is properly Son of the Father in both natures" (Council of Friuli).
Jesus is conceived by the Holy Spirit because he is the new Adam, "a life-giving spirit." He is the "man from heaven." From his conception, God gave to Jesus' humanity "the Spirit without measure" (Jn 3:34) so that "from his fullness, we can all receive" (Jn 1:16).
A New Era Begins (505-507)
By his virginal conception Jesus begins a new era, namely, the birth of children adopted by the Holy Spirit through faith. This new life comes not from "the will of the flesh nor the will of man, but of God" (Jn 1:16). Accepting this new life is virginal, a gift from the Spirit.
Mary's virginity is a sign of her own faith. As both virgin and mother, Mary is a perfect symbol for the Church who receives God's Word in faith and brings forth children in the Spirit.