As Christmas approaches, you hear the song "O Come, O Come, Emmanuel" sung at Mass at lot. Emmanuel means "God is with us." Christmas celebrates the coming of Christ, for he did come to us through Mary, but it won't do us any good if we do not let him into our hearts. Therefore, "O Come" must also be an invitation to ask the Lord to enter our hearts. We rejoice not only because God comes, but also because he is going to renew us, readying us for heaven.