The Responsorial Psalm is: "Fill me with your praise and I will sing your glory" (Psalm 71). We need to
praise God, celebrating what is good about him, or we will not appreciate his glory.
Judges 13: 2-25 tells us Samson was born of a woman who "had borne no children." But "an angel of the Lord appeared to the woman and said to her, 'Though you are barren and have had no children, yet you will conceive and bear a son."
This reminds us of the story of Sarah, the mother of Isaac (Genesis 11:30; 17: 15-19; 21: 1-3); Rebekah, the mother of Jacob (Genesis 25:21}; Rachel, the
mother of Jacob's sons Joseph and Benjamin (Genesis 29:31, 30: 22-24; 34:
16-18); Hannah, the mother of Samuel (1 Samuel 1: 2-20; and Elizabeth, the mother of John the Baptizer (Luke 1: 7-13). All of these women were barren, and by God's special intervention, all conceived sons who had a special role to play in the history of salvation. The barrenness of their mothers was the sign and proof that their birth was not just an ordinary human event, but due to a special intervention of God. This also said they were not just ordinary men, but ones specially chosen by God to do his work. This was the reason for the virginity of Mary. Jesus had to be born of a virgin so it would be clear he was the Son of God. In the absence of any human father, Mary's virginity was the sign and proof that the Father of Jesus was God.
But the O Antiphon reminds us that his mother was human: "Flower of Jesse's stem, sign of God's love for all his people, save us without delay!" Our salvation is the mystery of divinity made human and humanity made divine. God uses us to do his divine work. If we "fill our minds with praise of this mystery, our hearts will sing God's glory."
In Luke 1: 5-25 Zechariah, like Mary later, was "deeply disturbed" at the sight of the angel. But where Mary asked, "How can this be, since I am a virgin?" Zechariah asked, "How will I know that this is so?" and was reproached for his lack of faith.
We can't help wondering sometimes how God is going to fulfill his promises, but we must not doubt that he will. And if we do believe when what God promises seems humanly impossible, then we are experiencing a miracle already: the miracle of being empowered to believe what human reason is not adequate to explain. This is to experience God filling us with the divine power of grace. "Fill me with your praise" - as only you can - "and I will sing your glory."