The Collect for the Fourth Sunday of Advent in the Novus Ordo is also the Postcommunion for the Feast of the Annunciation (March 25) in the Extraordinary Form of the Roman Rite. The Annunciation was the moment of the Incarnation of our Lord.  Therefore, during Mass in the Ordinary Form on both Annunciation and Christmas, during the Creed of Holy Mass we bend our knees instead of merely bowing at the words “Et incarnatus est…” Alas, only on those two days do we kneel during the Creed with the Ordinary Form. If you recite the Angelus (which has an indulgence), you know today’s Collect. It was in the 8th-century Gelasian Sacramentary.