As we celebrate the Solemnity of the Annunciation we are really celebrating the Incarnation of the Eternal Word of God in flesh. Mary was told that she, a virgin, would conceive a Son. Mary, in asking how can this be since she, though engaged to Joseph, hoped to remain a virgin. She was not doubting God's plan but seeking how to be totally in line with his will. The angel implicitly assured her that it was God's plan that she should remain a virgin before, during and after childbirth. The conception will be by the power of the Holy Spirit and not by man. For the child to be born is not just any child, but the Son of the Most High God, sent to be the promised Messiah. 

Mary had been prepared for this gift-moment from the moment of her own conception. By God's mysterious grace Mary was conceived free from sin and remained such by grace all her life. This was in lieu of the fact that the child she was to conceive years later would come from a pure vessel of grace, with no taint of sin. If the Son of God would empty himself of his divinity to take on our flesh, he deserves the best human mother to be conceived in. Hail, Mary, full of grace, the Lord is with you!