The normal date for this Festival is March 25, nine months exactly before Christmas Day, but since March 25 was in Easter week in 2008, most churches transfer it to March 31, a Monday.
Let us look at the Collect in The BCP. It is a translation of what was the Post-Communion Prayer in the Latin Medieval Service according to the Sarum use/Rite.
The Reformers of the Church of England were not able to use the actual Collect in the Sarum Use because of its perceived doctrinal errors concerning the intercession of the Blessed Virgin Mary. Here it is in a traditional English rendering from the original Latin:
O God, who didst will thy Word to take flesh from the womb of the blessed Virgin, at the announcement of an angel: Grant unto us thy suppliants that, as we believe her to be the mother of God, so we may be assisted by her intercessions with thee, through the same, thy Son, Jesus Christ.
In contrast, the Collect that became the reformed Catholic Collect of the Anglican Way in The BCP is:
We beseech thee, O Lord, pour thy grace into our hearts; that, as have known the incarnation of thy Son Jesus Christ by the message of an angel, so by his cross and passion we may be brought unto the glory of his resurrection; through the same Jesus Christ our Lord.
In a more contemporary and modified form this could be:
Pour your grace, O Lord our God, into our hearts, that we may not be as those who received in vain from the angel the announcement of the Incarnation of your Son; but, being led by the Spirit, we may go on in faith to be conformed to his death and resurrection, through the same Jesus Christ our Lord.
In this Collect, the church speaks of the merciful, dynamic relation of the Father to his adopted children under the image of dew or rain, which descends to fertilize the heart and life. Further, the church utters a prayer for grace, not only to receive God’s message of reconciliation but also to be so established in it, as to be conformed by it to a suffering and glorified Lord and Savior.
The church also recalls the means used by God to communicate first with Mary and then with Joseph of Mary’s miraculous conception (which is the human side of the Incarnation of the Son). God sent an angel, probably Gabriel, the very same angel who had announced to Daniel the future advent of the Messiah (Daniel 9:21ff.).
The Incarnation, the taking to himself by the Son of God of our human nature in the womb of the Blessed Virgin Mary, makes it possible for him to the true Savior of the world, since he is both one with us and one with the Father. Therefore we come to the Father through union with him. We know these truths not merely as statements to be understood and learned, but also through faith and spiritual union with the Incarnate One himself.
We are brought to the glory of his resurrection by his cross and passion, and this in two ways. First, at the Cross he paid the ransom for our sins objectively as our Representative and Substitute, making for us a right and everlasting relation to the Father. And secondly, through our being conformed to his suffering in two ways— through the putting to death all sinful passions and thoughts in our hearts and by suffering patiently adversities, sickness, pain and tribulation.
The Festivals of the Blessed Virgin Mary in The BCP all point to her Son, who is her Lord concerning whom she once said: “Whatever he says to you, do it!”