“Hail, full of grace. The Lord is with you.”...“Behold the handmaid of the Lord; be it done to me according to thy word.”
Mary could not have known that her willingness to fulfill God's plan for her would reach so far. She, in her words, was a “lowly handmaiden” whom all generations would call “blessed”. In this, she became the mother of the Church, the Mother of us all. Rev. 12:17 makes it clear that she is our mother.
If she is our Mother, then we should give her the respect that she is due or we break the fifth commandment. Eph. 6:1-2 also makes it clear that this commandment refers not only to our biological father and mother, but to our spiritual ones as well.
Jesus could have come to us in different ways. He can do as he wishes. But he chose to work through Mary, and her cooperation in God's grace to mankind was the beginning of our salvation. Everything before this point is preparatory. Once Mary said “yes” Satan was defeated.