On Christmas Day billions of Christians worldwide join together with one voice to celebrate the Word become flesh. But when did the incarnation begin? Not on Christmas, but at the Annunciation (celebrated March 25, see Luke 1:26-38).
Think about it. Life begins at conception, thus the incarnation began when the Holy Spirit overshadowed the blessed Virgin. For nine months, wherever Mary went, God went. Jesus took His flesh from Mary and He dwelt among us in the womb of His Mother before appearing in Bethlehem. The Blessed Virgin was the Lord's throne before the manger.
No wonder all generations call Mary blessed just as she prophesied in Scripture.