Today is the Octave-Day of the Nativity, eight days since our Lord’s Birth, and in fulfillment of the ancient law, our Lord as a son of Abraham submitted himself to the Rite of Circumcision.
The 1962 Roman Missal reads:
In the Old Law, by the rite of Circumcision, every male Jew became a member and shared in the privileges and blessings of the chosen people of God. A Jew who failed to be initiated by the ceremony was excluded. Our Lord was Son of God by nature, and absolutely sinless, and therefore did not need adoption into the membership of God’s children. Yet, He submitted to the law. The Church also honours on this day the holy Name of Jesus, given to the Divine Child at the Circumcision, and the Divine Maternity of Our Lady.
Dom Prosper Guéranger adds:
Our new-born King and Saviour is eight days old to-day; the Star that guides the Magi is advancing towards Bethlehem, and five days hence will be standing over the Stable where our Jesus is being nursed by his Mother. To-day the Son of Man is to be circumcised; this first sacrifice of his innocent Flesh must honour the eighth day of his mortal life. To-day also a Name is to be given him: the name will be Jesus, and it means Saviour. So that mysteries abound on this day: let us not pass one of them over, but honour them with all possible devotion and love.
Moreover, the Gospel in the Extraordinary Form announces:
At that time, after eight days were accomplished that the Child should be circumcised: His Name was called Jesus, which was called by the Angel before he was conceived in the womb.
For Unto is a Child is born, and unto us a Son is given.