So the Child is circumcised. This is the child of whom it is said: Unto us a child is born, unto us a Son is given (Isa. 9:6), made under the law to redeem them that were under the law (Gal. 4:4).

[…] He that is circumcised in heart gains the protection of God, for the eyes of the Lord are upon the righteous (Ps. 33:16).

You will see that as all the ceremonies of the old law were types of realities in the new, so the circumcision of the body signified the cleansing of the heart from the guilt of sin.

But since the body and mind of man remain yet infected with a proneness to sin, the circumcision of the eighth day is also a type of that complete cleansing from sin which we shall have at the resurrection.

This ceremony was also performed in obedience to the commandment of God: Every male that opens the womb shall be called holy unto the Lord.

These words were written with especial reference to the delivery of the Blessed Virgin.

Truly He that opened her womb was holy, for He was altogether without spot.

And we may gather that the law was written specially for Him from the words of the Angel: That Holy Thing Which shall be born of thee, shall be called the Son of God.

Among all that are born of women the Lord Jesus Christ stood alone in holiness.

Fresh from His immaculate mirth, He felt no contagion from human corruption, and His heavenly majesty drove it away.

If we are to follow the letter and say that every male that opens the womb is holy, how shall we explain that so many have been unrighteous?

Was Ahab holy? Were the false prophets holy? Were they holy on whom Elijah justly called down fire from heaven?

But He to whom the sacred commandment of the law of God is mystically directed is the Holy One of Israel.

He also alone has opened the secret womb of His holy Virgin bride the Church, filling her with a sinless fruitfulness to give birth to Christian souls.

Ambrose of Milan (c.337-397): Commentary on St Luke, book 2 (from Mattins of In Circumcisione Domini in the Old Breviary.