We think of Christmas as the feast of the incarnation. But, since Orthodox Christians believe that life begins at conception, the incarnation really begins at the Annunciation, when Mary accepts the archangel’s news that she had been called by God to give birth to the Messiah.
What happens on December 25 is the fulfillment of something that begins nine months earlier, on March 25.
More info on the feast of the Annunciation of the Mother of God here.
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