Behold, you will conceive in your womb and bear a son, and you shall name him Jesus. It is exactly nine months nine months to the celebration of the birth of Jesus Christ. The Universal Church celebrates today the moment that set in motion the events that would lead to the birth of Jesus Christ. That moment has traditionally been referred to as the Annunciation. It was the moment when Archangel Gabriel told Mary she would be the Mother of the Son of God and she responded by saying may God’s will be done.
The Annunciation inaugurated the fullness of time, that is, the time for the fulfillment of God’s promises to creation (for the birth of Jesus Christ commenced the redemptive phase of the creative process). It was God’s plan right from the start that creation would find its final rest in the Creator. As an “outflow” of the Godhead, the creative work of God was to be complete when creation “makes” its way back to its source, the Godhead. However, this return, also known as salvation, was frustrated by the rebellion of creation. Blinded by the sin of man, creation became unable to make its way back to its Creator. God had to send a “guide” to the created world to help it make the return. Jesus Christ was that guide.
The Second Reading from the Letter to the Hebrews “celebrates” the person of Jesus Christ by reminding us of how he effected the work of redemption. Our first parents forfeited God’s redemptive plan for them when they chose to disobey God’s command. It was a choice that set the world on the path of self-annihilation. To remedy the sin of our first parents and to bring creation back onto the path of redemption, Christ had to undo what our first parents had done. Jesus Christ had to teach the world how to once again be obedient to God’s will. His coming to dwell amongst us was itself a result of Mary allowing the will of God to be done in her life.   
While the Annunciation is about the Lord, and rightly so, we can never speak about it without mentioning the name Mary. For it was upon Mary that the Holy Spirit descended in order to prepare a place for God to dwell. From the moment Mary said YES to the angel of the Lord, she became transformed into a vehicle of divine grace. No longer was Mary living for her own self but for her brothers and sisters. Her YES made it possible for God to assume a creaturely nature, dwell with his creatures as one of them, and by so doing effect the work of redemption of creation that was so crucial to the on-going creative process. Mary’s YES to the Lord earned her a special title of being a co-redeemer. It is a title that she has proudly merited. By saying YES to God, Mary, as it were, became a vehicle through which God’s blessings reached the universe. Through her consent to God’s plans, Mary took part in the whole redemptive work of her son, Jesus. It was from this moment that we celebrate today that Mary earned our veneration as the Mother of Christ and our Mother.