In Circumcisione Domini

Circumcision of Christ, Menologion of Basil II, 979–984.

From the Holy Gospel according to Luke
Luke 2:21
In that time, after eight days were accomplished, that the child should be circumcised, his name was called Jesus…

From the Sermons of Pope St. Leo the Great.
7th for Christmas
Dearly beloved brethren, whosoever will keep truly and honour piously this day's festival, it is necessary for him neither to think falsely of the Lord's Incarnation, nor meanly of the Lord's Godhead. For as there is danger, on the one hand, of denying the truth of Christ's participation of our nature, so is there no less danger, on the other, of doing despite to the equality of His glory with the glory of the Father. Wherefore, when we draw near to understand the mystery of Christ's Birth, wherein He was born of the Virgin Mary, we must leave the clouds of earthly imagination behind and pierce the fog of human wisdom with the eye of enlightened faith.

The authority on which we believe is the authority of God Himself; the teaching which we follow is the teaching of God Himself. Wherefore whether we lend the ear of our mind to the testimony of the Law, or to the revelations of the Prophets, or to the full pealing of the Gospel trumpet, that is true, which John the Son of Thunder, uttered, when he was filled with the Holy Ghost, and said: In the beginning was the Word, and the Word was with God, and the Word was God. The Same was in the beginning with God. All things were made by Him, and without Him was not anything made. True also is his witness when he saith: The Word was made Flesh, and dwelt among us, and we beheld His glory, the glory as of the Only-begotten of the Father. John i. 1-3, 14.

The Person of the Son of God therefore remaineth unchanged and one, though He have two natures, keeping His own, and taking ours. He appeareth as man to be the restorer of men, but abideth all the while in His immutable Godhead. That Godhead which He shareth with the Father was not a whit the less Almighty, nor did the form of a servant touch the form of God to derogate from it. The Most High and Everlasting Being, bending down for man's salvation, took the Manhood into His glory; He ceased not to be That which He is from everlasting. Hence we see the Only-begotten Son of God in one place confessing that the Father is greater than He, John xiv. 28, and in another declaring that He and the Father are One, x. 30. This is an evident proof of the distinction of His two natures, and the unity of His Person; for He is inferior to the Father as touching His Manhood, and yet equal to the Father as touching His Godhead, and yet, though He be God and Man, He is not two, but One Christ.

Lesson from the letter of St. Paul the Apostle to the Romans
Rom 4:1-17

1 What shall we say then that Abraham hath found, who is our father according to the flesh.
2 For if Abraham were justified by works, he hath whereof to glory, but not before God.
3 For what saith the scripture? Abraham believed God, and it was reputed to him unto justice.
4 Now to him that worketh, the reward is not reckoned according to grace, but according to debt.
5 But to him that worketh not, yet believeth in him that justifieth the ungodly, his faith is reputed to justice, according to the purpose of the grace of God.
6 As David also termeth the blessedness of a man, to whom God reputeth justice without works:

7 Blessed are they whose iniquities are forgiven, and whose sins are covered.

8 Blessed is the man to whom the Lord hath not imputed sin.

9 This blessedness then, doth it remain in the circumcision only, or in the uncircumcision also? For we say that unto Abraham faith was reputed to justice.

10 How then was it reputed? When he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision.
11 And he received the sign of circumcision, a seal of the justice of the faith, which he had, being uncircumcised; that he might be the father of all them that believe, being uncircumcised, that unto them also it may be reputed to justice:
12 And might be the father of circumcision; not to them only, that are of the circumcision, but to them also that follow the steps of the faithful, that is in the uncircumcision of our father Abraham.

13 For not through the law was the promise to Abraham, or to his seed, that he should be heir of the world; but through the justice of faith.
14 For if they who are of the law be heirs, faith is made void, the promise is made of no effect.
15 For the law worketh wrath. For where there is no law, neither is there transgression.
16 Therefore is it of faith, that according to grace the promise might be firm to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham, who is the father of us all,
17 As it is written: I have made thee a father of many nations, before God, whom he believed, who quickeneth the dead; and calleth those things that are not, as those that are.

From the Sermons of Pope St. Leo the Great.
7th for Christmas
Dearly beloved brethren, whosoever will keep truly and honour piously this day's festival, it is necessary for him neither to think falsely of the Lord's Incarnation, nor meanly of the Lord's Godhead. For as there is danger, on the one hand, of denying the truth of Christ's participation of our nature, so is there no less danger, on the other, of doing despite to the equality of His glory with the glory of the Father. Wherefore, when we draw near to understand the mystery of Christ's Birth, wherein He was born of the Virgin Mary, we must leave the clouds of earthly imagination behind and pierce the fog of human wisdom with the eye of enlightened faith.

The authority on which we believe is the authority of God Himself; the teaching which we follow is the teaching of God Himself. Wherefore whether we lend the ear of our mind to the testimony of the Law, or to the revelations of the Prophets, or to the full pealing of the Gospel trumpet, that is true, which John the Son of Thunder, uttered, when he was filled with the Holy Ghost, and said: In the beginning was the Word, and the Word was with God, and the Word was God. The Same was in the beginning with God. All things were made by Him, and without Him was not anything made. True also is his witness when he saith: The Word was made Flesh, and dwelt among us, and we beheld His glory, the glory as of the Only-begotten of the Father. John i. 1-3, 14.

The Person of the Son of God therefore remaineth unchanged and one, though He have two natures, keeping His own, and taking ours. He appeareth as man to be the restorer of men, but abideth all the while in His immutable Godhead. That Godhead which He shareth with the Father was not a whit the less Almighty, nor did the form of a servant touch the form of God to derogate from it. The Most High and Everlasting Being, bending down for man's salvation, took the Manhood into His glory; He ceased not to be That which He is from everlasting. Hence we see the Only-begotten Son of God in one place confessing that the Father is greater than He, John xiv. 28, and in another declaring that He and the Father are One, x. 30. This is an evident proof of the distinction of His two natures, and the unity of His Person; for He is inferior to the Father as touching His Manhood, and yet equal to the Father as touching His Godhead, and yet, though He be God and Man, He is not two, but One Christ.