Catechism of the Catholic Church
496 From the first formulations of her faith, the Church has confessed that Jesus was conceived solely by the power of the Holy Spirit in the womb of the Virgin Mary, affirming also the corporeal aspect of this event: Jesus was conceived "by the Holy Spirit without human seed". 146 The Fathers see in the virginal conception the sign that it truly was the Son of God who came in a humanity like our own. Thus St. Ignatius of Antioch at the beginning of the second century says:
You are firmly convinced about our Lord, who is truly of the race of David according to the flesh, Son of God according to the will and power of God, truly born of a virgin,. . . he was truly nailed to a tree for us in his flesh under Pontius Pilate. . . he truly suffered, as he is also truly risen. 147
497 The Gospel accounts understand the virginal conception of Jesus as a divine work that surpasses all human understanding and possibility: 148 "That which is conceived in her is of the Holy Spirit", said the angel to Joseph about Mary his fiancee. 149 The Church sees here the fulfilment of the divine promise given through the prophet Isaiah: "Behold, a virgin shall conceive and bear a son." 150
498 People are sometimes troubled by the silence of St. Mark's Gospel and the New Testament Epistles about Jesus' virginal conception. Some might wonder if we were merely dealing with legends or theological constructs not claiming to be history. To this we must respond: Faith in the virginal conception of Jesus met with the lively opposition, mockery or incomprehension of non-believers, Jews and pagans alike; 151 so it could hardly have been motivated by pagan mythology or by some adaptation to the ideas of the age. The meaning of this event is accessible only to faith, which understands in it the "connection of these mysteries with one another" 152 in the totality of Christ's mysteries, from his Incarnation to his Passover. St. Ignatius of Antioch already bears witness to this connection: "Mary's virginity and giving birth, and even the Lord's death escaped the notice of the prince of this world: these three mysteries worthy of proclamation were accomplished in God's silence." 153
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.