Mary, The Mother of God The Mother of God

During the Twelve Days of Christmas the Church celebrates many important feasts. None, however, is as important as the feast celebrated on the octave (eighth day) of Christmas, January 1: the Solemnity of Mary, the Mother of God. In fact, the Church regards this feast as so important that it is a Holy Day of Obligation. On this day, we are reminded of the role that the Blessed Virgin played in the plan of our salvation. Christ's Birth was made possible by Mary's fiat: "Be it done unto me according to Thy word."
One of the earliest titles given by Christians to the Blessed Virgin was Theotokos "God-bearer." We celebrate her as the Mother of God, because, in bearing Christ, she bore the fullness of the Godhead within her.
 As we begin another year, we draw inspiration from the selfless love of the Theotokos, who never hesitated to do the will of God. And we trust in her prayers to God for us, that we might, as the years pass, become more like her. O Mary, Mother of God, pray for us!
 (excerpt catholicism.about.com)