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 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