The Annunciation, Henry Ossawa Tanner (1898). The Feast of the Annunciation, contemporarily the Solemnity of the Annunciation, commemorates the visit of the angel Gabriel to the Virgin Mary, during which he informed her that she would be the mother of Jesus Christ, the Son of God.It is celebrated on 25 March each year.t is a principal Marian feast, classified as a solemnity in the Catholic Church. Two examples in Catholicism of the importance attached to the Annunciation are the Angelus prayer, and the event's position as the first Joyful Mystery of the Rosary.