At that time, the angel Gabriel was sent from God into a city of Galilee, called Nazareth, to a virgin espoused to a man whose name was Joseph, of the house of David: and the virgin's name was Mary. And the angel being come in, said unto her: "Hail, full of grace, the Lord is with thee: blessed art thou among women" (Luke 1:26-28).
The Church holds this day in such high esteem, it's marked on the Liturgical Calendar as a Solemnity, meaning, essentially, these days are just as important as Sundays, the Lord's Day. In a side note, that also means Catholics are free to eat meat! To mark the day, here is my favourite recipe for the most perfect prime rib, by Chef John at Food Wishes.com: