Zechariah, the husband of Elizabeth and father of John the Baptist, for doubting the word of the angel, had been struck dumb but when, at the circumcision of his son, he confirmed that the boy's name would be John, he recovered his speech and broke out into this song of praise. In it he thanks God for having "visited his people" and "come to their rescue" just has he had promised through the mouths of the prophets down the ages.
Zechariah goes on to speak of his newly-born son, "You will be called Prophet of the Most High, for you will go before the Lord to prepare the way for Him." That will be John's special role, to prepare us for the coming of Jesus our Saviour. It is also the role given to each one of us by our Baptism.
The first reading from the Second Book of Samuel speaks of God asking David to make him a dwelling place worthy of him. David the king lives in a palace of fine cedar wood while God only has a tent, the tent where the Ark of the Covenant was kept. The implication of this passage for us in today's Mass is that Mary, the mother of Jesus, is the new temple where God lives, she is the new Ark of the Covenant - a fitting place, a place of perfection without any trace of sin or evil. But later on, Paul will remind Christians that each one of them, too, is now a temple of God, of the Spirit of Jesus. In the New Covenant there is no longer any temple building but "you are God's temple".
O Prince of Peace, come and take up Your abode in my heart.