11 And unto what are You born? “The Lord has sworn, and will not repent: You are a Priest for ever after the order of Melchizedec”. For unto this were You born from the womb before the morning star, that You might be a Priest for ever after the order of Melchizedec. For in that character in which He was born of the Father, God with God, coeternal with Him who begot Him, He is not a Priest; but He is a Priest on account of the flesh which He assumed, on account of the victim which He was to offer for us received from us. “The Lord,” then, “has sworn.” What then means, the Lord has sworn? Does the Lord, who forbids men to swear, Himself swear? Or does He possibly forbid man to swear chiefly on this account, that he may not fall into perjury, and for this reason the Lord may swear, since He cannot be forsworn. For man, who, through a habit of swearing, may slip into perjury, is rightly forbidden to swear: for he will be farther from perjury in proportion as he is far from swearing. For the man who swears, may swear truly or falsely: but he who swears not, cannot swear falsely; for he swears not at all. Why then should not the Lord swear, since the Lord's oath is the seal of the promise? Let Him swear by all means. What then do you, when you swear? You call God to witness: this is to swear, to call God to witness; and for this reason there must be anxiety, that you may not call God to witness anything false. If therefore thou by an oath dost call God to witness, why then should not God also call Himself to witness with an oath? “I live, says the Lord,” this is the Lord's oath....“The Lord swore,” then, that is, confirmed: “He will not repent,” He will not change. What? You are a Priest for ever. “For ever,” for He will not repent. But Priest, in what sense? Will there be those victims, victims offered by the Patriarchs, altars of blood, and tabernacle, and those sacred emblems of the Old Covenant? God forbid! These things are already abolished; the temple being destroyed, that priesthood taken away, their victim and their sacrifice having alike disappeared, not even the Jews have these things. They see that the priesthood after the order of Aaron has already perished, and they do not recognise the Priesthood after the order of Melchizedec. I speak unto believers. If catechumens understand not something, let them lay aside sloth, and hasten unto knowledge. It is not therefore needful for me to disclose mysteries here: let the Scriptures intimate to you what is the Priesthood after the order of Melchizedec.
12. “The Lord on Your right hand”. The Lord had said, “Sit on My right hand;” now the Lord is on His right hand, as if they changed seats....That very Christ, the “Lord on Your right hand,” unto whom You have sworn, and it will not repent You: what does He, Priest for evermore? What does He, who is at the right hand of God, and intercedes for us, like a priest entering into the inner places, and into the holy of holies, into the mysteries of heaven, He alone being without sin, and therefore easily purifying from sins. He therefore “on Your right hand shall wound even kings in the day of His wrath.” What kings, do you ask? Have you forgotten? “The kings of the earth stood up, and the rulers took counsel together against the Lord, and against His Anointed.” These kings He wounded by His glory, and by the weight of His Name made kings weak, so that they had not power to effect what they wished. For they strove amain to blot out the Christian name from the earth, and could not; for “Whosoever shall fall on this stone shall be broken.” Kings therefore fall on this “stone of offense,” and are therefore wounded, when they say, Who is Christ? I know not what Jew or what Galilean He may have been, who died, who was slain in such a manner! The stone is before your feet, lying, so to speak, mean and humble: therefore by scorning thou dost stumble, by stumbling you fall, by falling you are wounded....“But on whomsoever it shall fall, it will grind him to powder.” When therefore any one falls upon it, it lies as it were low; it then wounds: but when it shall grind him to powder, then it will come from above. See how in these two words, it shall wound him and grind him to powder: he strikes upon it, and it shall come down upon him: are distinguished the two seasons, of the humiliation and the majesty of Christ, of hidden punishment and future judgment. He will not crush, when He comes, that man whom He does not wound when He lies in a contemptible appearance....
13. “He shall judge among the heathen: He shall fill up what has fallen”. Whoever you are who art obstinate against Christ, you have raised on high a tower that must fall. It is good that you should cast yourself down, become humble, throw yourself at the feet of Him who sits on the right hand of the Father, that in you a ruin may be made to be built up. For if you abide in your evil height, you shall be cast down when you can not be built up. For of such the Scripture says in another passage: “Therefore shall He break down, and not build them up.” Beyond doubt he would not say this of some, unless there were some whom He broke down so as to build them up again. And this is going on at this time, while Christ is judging among the heathen in such a manner as to fill up what has fallen. “He shall smite many heads over the earth.” Here upon the earth in this life He shall smite many heads. He makes them humble instead of proud; and I dare to say, my brethren, that it is more profitable to walk here humbly with the head wounded, than with the head erect to fall into the judgment of eternal death. He will smite many heads when he causes them to fall, but He will fill them up and build them up again.
14. “He shall drink of the brook in the way, therefore shall he lift up his head”. Let us consider Him drinking of the brook in the way: first of all, what is the brook? The onward flow of human mortality: for as a brook is gathered together by the rain, overflows, roars, runs, and by running runs down, that is, finishes its course; so is all this course of mortality. Men are born, they live, they die, and when some die others are born, and when they die others are born, they succeed, they flock together, they depart and will not remain. What is held fast here? What does not run? What is not on its way to the abyss as if it was gathered together from rain? For as a river suddenly drawn together from rain from the drops of showers runs into the sea, and is seen no more, nor was it seen before it was collected from the rain; so this hidden rain is collected together from hidden sources, and flows on; at death again it travels where it is hidden: this intermediate state sounds and passes away. Of this brook He drinks, He has not disdained to drink of this brook; for to drink of this brook was to Him to be born and to die. What this brook has, is birth and death; Christ assumed this, He was born, He died. “Therefore has He lifted up His head;” that is, because He was humble, and “became obedient unto death, even the death of the Cross: therefore God also has highly exalted Him, and given Him a Name which is above every name; that at the Name of Jesus every knee shall bow, of things in Heaven, and things in earth, and things under the earth; and that every tongue shall confess that Jesus Christ the Lord is in the glory of God the Father.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)