O Adonai is today’s O Antiphon heard before the Gospel reading at Mass and the Magnificat at Evening Prayer.
From now until 22 December there will be an O Antiphon as the Messiah is daily called by an Old Testament title.
Today 18 December is known as the Expectation of Mary, or Our Lady of the O, as it falls during the O Antiphons week.
The day was first observed at Toledo as part of the Mozarabic rite in 656 dates from the 6th century. The O Antiphons emerged a century later.
As we think of Mary and Joseph leaving Nazareth about now for their long walk to Bethlehem, with a donkey maybe, so the Expectation of Mary recalls why they are setting out.
They need to be settled somewhere before Mary gives birth to the Christ Child.
So today is another opportunity, like the Translation of the Holy House on 10 December, to recall the Annunciation.
In some parishes there is a Posada custom with the figures of Mary and Joseph moving from house to house until arriving at the crib scene in church on Christmas Eve.