16 In all these things shall we not rejoice? Or shall we contain our joy? Or shall words suffice for our gladness? Or shall the tongue be able to express our rejoicing? If therefore no words suffice, “Blessed is the people, O Lord, that knows glad shouting”. O blessed people! Do you conceive aright, do you understand, glad shouting? For except thou understand glad shouting, you can not be blessed. What do I mean by understanding glad shouting? Whether you know the source of that rejoicing which is beyond words to express. For this joy is not of yourself, since “he that glories, let him glory in the Lord.” Rejoice not then in your own pride, but in God's grace. See that that grace is such, that the tongue fails to express its greatness, and then you understand glad shouting....O Lord, “they shall walk in the light of Your countenance.” “They shall rejoice in Your name all the day”. That Thabor and Hermon shall rejoice in Your name: all day shall they rejoice, if they will, in Your name; but if they will rejoice in their own name, they shall not rejoice all day: for they shall not continue in their joy, when they shall delight in themselves, and fall through pride. That they may rejoice all day, therefore, “they shall rejoice in Your name, and in Your righteousness shall they be exalted.” Not in their own, but in Yours: lest they have a zeal of God, but not according to knowledge. For some are noted by the Apostle, that they have a zeal of God, but not according to knowledge, “being ignorant of God's righteousness, and going about to establish their own,” and not rejoicing in Your light, and thus “not submitting themselves unto the righteousness of God.” And why? Because “they have a zeal of God, but not according to knowledge.” But the people who knows glad shouting (for the former err from want of knowledge, but blessed is the people not that knows not, but that knows glad shouting), whence ought it to shout, whence to rejoice, but in Your name, walking in the light of Your countenance? And it shall deserve to be exalted, but in Your righteousness: let every man take away altogether his own righteousness, and be trembled: the righteousness of God shall come, and he shall be exalted, “and in Your righteousness shall they be exalted.”
17. “For You are the glory of their strength: and in Your good pleasure You shall lift up our horns”: because it has seemed good to You, not because we are worthy.
18. “For of the Lord is our taking up”. For I was moved like a heap of sand, that I might fall; and I should have fallen, had not the Lord taken me up. “For of the Lord is (our) taking up: and of the Holy One of Israel our King.” Himself is your taking up, Himself your illumination: in His light you are safe, in His light you walk, in His righteousness you are exalted. He took you up, He guards your weakness: He gives you strength of Himself, not of yourself.
19. “You spoke sometime in vision unto Your sons, and said”. You spoke in your vision. You revealed this to Your Prophets. For this reason You spoke in vision, that is, in revelation: whence Prophets were called seers. They saw something within, which they were to speak without: and secretly they heard what they preached openly. Then “You spoke in vision unto Your sons, and said, I have laid help upon One that is mighty.” You understand Who is meant by mighty? “I have exalted One chosen out of the people.” And Who is meant by chosen? One who, you rejoice, is already exalted.
20. “I have found David My servant:” that David from David's seed: “with My holy oil have I anointed Him”: for it is said of Him, “God, even Your God, has anointed You with the oil of gladness above Your fellows.”
21. “My hand shall hold Him fast, and My arm shall strengthen Him”: because there was a taking up of man; because flesh was assumed in the Virgin's womb, because by Him who in the form of God is coequal with the Father, the form of a servant was taken, and He became obedient unto death, even the death of the Cross.
22. “The enemy shall not be able to do him violence”. The enemy rages indeed but he shall not be able to do Him violence: he is wont to hurt, but he shall not hurt. How then shall he afflict Him? He will exercise Him, but he shall not hurt Him. There shall be profit in his raging; for those against whom he rages shall be crowned in their conquering. For how is he conquered, if he rages not against us? Or where is God our helper, if we fight not? The enemy therefore shall do what is in his power; but “he shall not be able to do Him violence: the son of wickedness shall not come near to hurt Him.”
23. “I will cut in pieces His enemies before His face”. They are cut in pieces from their conspiracy, and in that they believe they are cut in pieces; for they believe by degrees; as when the calf's head was ground small, they will come to be the drink of God's people. For Moses ground down the calf's head, and sprinkled it upon the water, and made the children of Israel drink it. All the unbelieving are ground: they believe by degrees; and they are drunk by the people of God, and pass into Christ's body. “I will cut in pieces His foes before His face: and put to flight them that hate Him.”
24. “My truth also and My mercy is with Him”. All the paths of the Lord are mercy and truth. Remember, as much as you can, how often these two attributes are urged upon us, that we render them back to God. For as He showed us mercy that He might blot out our sins, and truth in fulfilling His promises; so also we, walking in His path, ought to give back to Him mercy and truth; mercy, in pitying the wretched; truth, in not judging unjustly. Let not truth rob you of mercy, nor mercy hinder truth: for if through mercy you shall have judged contrary to truth, or by rigorous truth shall have forgotten mercy, you will not be walking in the path of God, where “mercy and truth meet together.” “And in My name shall His horn be exalted.” Why should I say more? You are Christians, recognise Christ.
25. “I will set His hand also in the sea”: that is, He shall rule over the Gentiles; “and His right hand in the floods.” Rivers run into the sea: avaricious men roll onwards into the bitterness of this world: yet all these kinds of men will be subject to Christ.
26. “He shall call me, You are My Father, and the lifter up of My salvation”.
“And I will make Him my first-born; higher than the kings of the earth”. Our Martyrs, whose birthdays we are celebrating, shed their blood on account of these things, which were believed though not yet seen; how much more brave ought we to be, as we see what they believed? For they had not yet seen Christ raised on high among the kings of the earth: as yet princes were taking counsel together against the Lord and His Anointed: what follows in the same Psalm was not then fulfilled, “Be wise now therefore, O you kings: be learned, you that are judges of the earth.” Now indeed Christ has been exalted among the kings of the earth.
27. “My mercy will I keep for Him for ever: and my Testament faithful with Him”. On His account, the Testament is faithful: in Him the Testament is mediated: He is the Sealer, the Mediator of the Testament, the Surety of the Testament, the Witness of the Testament, the Heritage of the Testament, the Coheir of the Testament.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)