"Mary remained with her about three months" (Luke 1:56).
It's called the Visitation: when Mary, pregnant with our Lord, visited the much older Elizabeth, pregnant with John the Baptist (about six months older than Christ). And it looks like Mary spent roughly the first trimester of her pregnancy visiting Elizabeth: helping her, serving her, preparing for the birth of John.
If that is correct, then it was during the Visitation that the heart of our Lord took shape and began to beat. The same heart that would stop beating on the cross. During the Visitation that His face got its eyes, ears, nose, and mouth. The same mouth that would say, "Take heart, child, your sins are forgiven" (Matt. 9:2).
We think much about the birth of our dear Lord. And well we should! But let us think some more about His nine months in the womb of the blessed virgin Mary.
Mary visited Elizabeth with Christ inside of her. Holy Communion means that Christ is inside of you and that you may go and serve your spouse, children, neighbor, and especially the one in need this Christmas time.
Holy Baptism puts us inside of Christ. Holy Communion puts Christ inside of us. And all that is left is to love.