The most Blessed Virgin Mary was, from the first moment of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Saviour of the human race, preserved immune from all stain of original sin. 135
Catechism number 503
Mary's virginity manifests God's absolute initiative in the Incarnation. Jesus has only God as Father. "He was never estranged from the Father because of the human nature which he assumed. . . He is naturally Son of the Father as to his divinity and naturally son of his mother as to his humanity, but properly Son of the Father in both natures."161