What sort of sign were the shepherds given? You will find the child wrapped in swaddling clothes and lying in a manger. . . .What kind of sign, then, can this be?
Indeed it is a great one, if only we understand it rightly. Such understanding will be ours if this message of love is not restricted to our hearing, but if our hearts too are illuminated by the light which accompanied the appearance of the angels. The angel who first proclaimed the good tidings appeared surrounded by light to teach us that only those whose minds are spiritually enlightened can truly understand the message.
Much can be said of this sign; but as time is passing, I shall say little, and briefly. Bethlehem, the house of bread, is holy Church, in which is distributed the body of Christ, the true bread. The manger at Bethlehem is the altar of the church; it is there that Christ's creatures are fed. This is the table of which it is written, You have prepared a banquet for me. In this manger is Jesus, wrapped in the swaddling clothes which are the outward form of the sacraments. Here in this manger, under the species of bread and wine, is the true body and blood of Christ. We believe that Christ himself is here, but he is wrapped in swaddling clothes; in other words, he is invisibly contained in these sacraments. We have no greater or clearer proof of Christ's birth than our daily reception of his body and blood at the holy altar, and the sight of him who was once born for us of a virgin daily offered in sacrifice for us.
Christmas Discourse, Aelred of Rievaulx