The feast of the Annunciation goes back to the fourth or fifth century. 
Now, as Luke 1:26-38 tells us, the decision is being realized.
The God-Man embraces all humanity, indeed all creation, to bring it to God in one great act of love. Because human beings have rejected God, Jesus will accept a life of suffering and an agonizing death: “No one has greater love than this, to lay down one’s life for one’s friends” (John 15:13).
Mary has an important role to play in God’s plan. From all eternity God destined her to be the mother of Jesus and closely related to him in the creation and redemption of the world. We could say that God’s decrees of creation and redemption are joined in the decree of Incarnation. Because Mary is God’s instrument in the Incarnation, she has a role to play with Jesus in creation and redemption. It is a God-given role. It is God’s grace from beginning to end. Mary becomes the eminent figure she is only by God’s grace. She is the empty space where God could act. Everything she is she owes to the Trinity.
She is the virgin-mother who fulfills Isaiah 7:14 in a way that Isaiah could not have imagined. She is united with her son in carrying out the will of God (Psalm 40:8-9; Hebrews 10:7-9; Luke 1:38).
Together with Jesus, the privileged and graced Mary is the link between heaven and earth. She is the human being who best, after Jesus, exemplifies the possibilities of human existence. She received into her lowliness the infinite love of God. She shows how an ordinary human being can reflect God in the ordinary circumstances of life. She exemplifies what the Church and every member of the Church is meant to become. She is the ultimate product of the creative and redemptive power of God. She manifests what the Incarnation is meant to accomplish for all of us.
. The central focus of this Solemnity is the Incarnation: God has become one of us. From all eternity God had decided that the Second Person of the Blessed Trinity should become human.){kind=link}
is it a holy day of obligation?
On December 13, 1991 the members of the National Conference of Catholic Bishops of the United States of American made the following general decree concerning holy days of obligation for Latin rite Catholics:
In addition to Sunday, the days to be observed as holy days of obligation in the Latin Rite dioceses of the United States of America, in conformity with canon 1246, are as follows:
1) January 1, the solemnity of Mary, Mother of God
2) Thursday of the Sixth Week of Easter, the solemnity of the Ascension
3) August 15, the solemnity of the Assumption of the Blessed Virgin Mary
4) November 1, the solemnity of All Saints
5) December 8, the solemnity of the Immaculate Conception
6) December 25, the solemnity of the Nativity of Our Lord Jesus Christ [list numbers are not in original]
Whenever January 1, the solemnity of Mary, Mother of God, or August 15, the solemnity of the Assumption, or November 1, the solemnity of All Saints, falls on a Saturday or on a Monday, the precept to attend Mass is abrogated.
This day when 2000 years ago, angel Gabriel appeared to Mary.
And in the year of 1997, I was born!!
Now in 2012, here I am seeking for God grace to live my life according to his holy wish.