:
1 The king shall joy in thy strength, O LORD; and in thy salvation how greatly shall he rejoice! 2 Thou hast given him his heart's desire, and hast not withholden the request of his lips. Selah. 3 For thou preventest him with the blessings of goodness: thou settest a crown of pure gold on his head. 4 He asked life of thee, and thou gavest it him, even length of days for ever and ever. 5 His glory is great in thy salvation: honour and majesty hast thou laid upon him. 6 For thou hast made him most blessed for ever: thou hast made him exceeding glad with thy countenance. 7 For the king trusteth in the LORD, and through the mercy of the most High he shall not be moved. 8 Thine hand shall find out all thine enemies: thy right hand shall find out those that hate thee. 9 Thou shalt make them as a fiery oven in the time of thine anger: the LORD shall swallow them up in his wrath, and the fire shall devour them. 10 Their fruit shalt thou destroy from the earth, and their seed from among the children of men. 11 For they intended evil against thee: they imagined a mischievous device, which they are not able to perform. 12 Therefore shalt thou make them turn their back, when thou shalt make ready thine arrows upon thy strings against the face of them. 13 Be thou exalted, LORD, in thine own strength: so will we sing and praise thy power.
[AD 339] Eusebius of Caesarea on Psalms 21:1
I think that these words had been prophesied by those who had spoken long before David. Since David had learned from the lofty oracles that those words were looking not only at the strength of his own salvation but also that which was going to come forth from his seed, concerning which he said he would rejoice and praise with enthusiasm. Having been assured of those things and the enemies having been thoroughly subjugated with mighty power, to you, God, the author of the victory, he grants the prize of his victory. And he rejoices and praises as he is snatched from the snares of the enemies, nor does he rejoice so much in his own deliverance as in that salvation sent from you. As he seeks your deliverance with lofty vows from his own lips, he will entreat you often for the advent of his deliverance; his prayer frequently uttered, he never fails in hope, nor will his request be in vain.

[AD 430] Augustine of Hippo on Psalms 21:1
"O Lord, the King shall rejoice in Your strength" [Psalm 21:1]. O Lord, in Your strength, whereby the Word was made flesh, the Man Christ Jesus shall rejoice. "And shall exult exceedingly in Your salvation." And in that, whereby Thou quickenest all things, shall exult exceedingly.

[AD 585] Cassiodorus on Psalms 21:1
Our belief that there are two natures in Christ the Lord, one divine and one human, is a matter of salvation. These two natures endure without change in one person for ever. This statement of faith bears frequent repetition, because, when it is frequently heard and believed, it brings life. In the initial narrative of this psalm, the words of the prophet are directed toward God the Father concerning the Lord’s incarnation. The second part describes his diverse virtues and glory, describing his life from the point at which he suffered until he attained the height and peak of all things by the Father’s gracious gift. In the third, the same prophet turns to the Lord Christ, and here in the manner of those who make wishes, he asks that what he knows is to come will be done at the judgment.

[AD 9999] Pseudo-Athanasius on Psalms 21:1
Friends of David also delivered this psalm, as if he were now pleased for the salvation that was born from his seed for the world; this was a glorious crown for him, and length of days and glory and magnificence, and delight and joy and hope and unshakeable grace.

[AD 339] Eusebius of Caesarea on Psalms 21:2
Having prophesied the promises made earlier to David, he then explains the reason why these things are going to happen. For what is that reason unless hope in God in which the one who has received mercy does not falter and in that very hope granted by God most high he does not waver from a firm and steady foundation?

[AD 430] Augustine of Hippo on Psalms 21:2
"You have given Him the desire of His soul" [Psalm 21:2]. He desired to eat the Passover, [Luke 22:15] and to lay down His life when He would, and again when He would to take it; and You have given it to Him. [John 10:18] "And hast not deprived Him of the good pleasure of His lips." "My peace," says He, "I leave with you:" [John 14:27] and it was done.

[AD 399] Evagrius Ponticus on Psalms 21:3
Christ is the crown of the rational nature.

[AD 420] Jerome on Psalms 21:3
The crown of the Lord is the church gathered from the various nations, about which Paul in the person of the believers says, “My joy and my crown.”

[AD 430] Augustine of Hippo on Psalms 21:3
"For You have presented Him with the blessings of sweetness" [Psalm 21:3]. Because He had first quaffed the blessing of Your sweetness, the gall of our sins did not hurt Him. " Diapsalma. You have set a crown of precious stone on His Head." At the beginning of His discoursing precious stones were brought, and compassed Him about; His disciples, from whom the commencement of His preaching should be made.

[AD 430] Augustine of Hippo on Psalms 21:3
And what is here more fitly understood than that very desire of good of which we are speaking? For good begins then to be longed for when it has begun to grow sweet. But when good is done by fear of penalty, not by the love of righteousness, good is not yet well done. Nor is that done in the heart that seems to be done in the act, when a person would rather not do it if he could evade it with impunity. Therefore the “blessing of sweetness” is God’s grace, by which is caused in us that what he prescribes to us delights us, and we desire it—that is, we love it; in which if God does not precede us, not only is it not perfected but it is not even begun, from us. For if without him we are able to do nothing, we are able neither to begin nor to perfect, because to begin, it is said, “His mercy shall prevent me”; to finish, it is said, “His mercy shall follow me.”

[AD 585] Cassiodorus on Psalms 21:3
He indicates that humanity is ever adorned with the anticipatory grace of the Godhead, because no one offers anything to God first unless what is good is granted by a heavenly gift.

[AD 202] Irenaeus on Psalms 21:4
It is the Father of all who imparts continuance forever and ever on those who are saved. For life does not arise from us nor from our own nature, but it is bestowed according to the grace of God.

[AD 430] Augustine of Hippo on Psalms 21:4
"He asked life; and You gave Him:" He asked a resurrection, saying, "Father, glorify Your Son;" [John 17:1] and You gave it Him, "Length of days for ever and ever" [Psalm 21:4]. The prolonged ages of this world which the Church was to have, and after them an eternity, world without end.

[AD 460] Arnobius the Younger on Psalms 21:4
He sought life; he lived as a man. Having been limited in life, in death he received length of days not just to old age but to eternity.

[AD 430] Augustine of Hippo on Psalms 21:5
"His glory is great in Your salvation" [Psalm 21:5]. Great indeed is His glory in the salvation, whereby You have raised Him up again. "Glory and great honour shall Thou lay upon Him." But You shall yet add unto Him glory and great honour, when You shall place Him in heaven at Your right hand.

[AD 460] Arnobius the Younger on Psalms 21:5
Great is his glory. In what way is it great? Not in the assumption of deity but in the salvation of humanity.

[AD 430] Augustine of Hippo on Psalms 21:6
"For You shall give Him blessing for ever and ever." This is the blessing which You shall give Him for ever and ever: "You shall make Him glad in joy together with Your countenance" [Psalm 21:6]. According to His manhood, You shall make Him glad together with Your countenance, which He lifted up to You.

[AD 430] Augustine of Hippo on Psalms 21:7
"For the King hopes in the Lord." For the King is not proud, but humble in heart, he hopes in the Lord. "And in the mercy of the Most Highest He shall not be moved" [Psalm 21:7]. And in the mercy of the Most Highest His obedience even unto the death of the Cross shall not disturb His humility.

[AD 460] Arnobius the Younger on Psalms 21:7
For that reason you placed glory and great honor on him, and you gave him eternal blessing, because he hoped in the Lord and in his mercy he was not deeply disturbed.

[AD 430] Augustine of Hippo on Psalms 21:8
"Let Your hand be found by all Your enemies." Be Your power, O King, when You come to judgment, found by all Your enemies; who in Your humiliation discerned it not. "Let Your right hand find out all that hate You" [Psalm 21:8]. Let the glory, wherein Thou reign at the right hand of the Father, find out for punishment in the day of judgment all that hate You; for that now they have not found it.

[AD 460] Arnobius the Younger on Psalms 21:8
From the place [of exaltation] the Father says to his Son, “Let your hand be found by all your enemies; let your right, which received the nails on the cross, find those who hated you; discard them as earthen vessels in a fire in the time of your appearance. Then in your wrath you will throw them into disorder, and the fire will devour them.”

[AD 585] Cassiodorus on Psalms 21:8
They are only called enemies as long as they are led astray by the devil’s enticements. But when they return to Christ the Lord, they are called servants, children and friends.

[AD 430] Augustine of Hippo on Psalms 21:9
"You shall make them like a fiery oven:" You shall make them on fire within, by the consciousness of their ungodliness: "In the time of Your countenance:" in the time of Your manifestation. "The Lord shall trouble them in His wrath, and the fire shall devour them" [Psalm 21:9]. And then, being troubled by the vengeance of the Lord, after the accusation of their conscience, they shall be given up to eternal fire, to be devoured.

[AD 585] Cassiodorus on Psalms 21:9
An oven is a round structure made of bronze for baking bread.… Sinners are rightly compared with it, since at the coming judgment they will be tormented both with mental grief and with punitive pain, because with a stubborn mind they have lived in opposition to the Lord’s laws. The time of the Lord’s anger is the day of judgment when the Son of Man will be seen by all, but only the righteous will look on him also through the contemplation of his divinity.… Earlier, in praise for the Lord Christ, the psalmist described the honor and glory of Christ through the diverse character of his graces. Now … he says that his enemies will be afflicted with various punishments so that they might be rendered as disgusting as he is marvelous.… They will be sentenced to be devoured by undying flames. No delay accompanies the Lord’s command, but as soon as he determines it, it is completed.

[AD 339] Eusebius of Caesarea on Psalms 21:10
But the seed of the godless and the fruit of the wicked are their words, teachings and unrighteous writings, which they have disseminated through people after they are forgotten. God, being good, scatters each one and destroys them from the midst so that neither the fruit nor the seed of the wicked remains.

[AD 430] Augustine of Hippo on Psalms 21:10
"Their fruit shall You destroy out of the earth." Their fruit, because it is earthly, shall You destroy out of the earth. "And their seed from the sons of men" [Psalm 21:10]. And their works; or, whomsoever they have seduced, You shall not reckon among the sons of men, whom You have called into the everlasting inheritance.

[AD 430] Augustine of Hippo on Psalms 21:11
"Because they turned evils against You." Now this punishment shall be recompensed to them, because the evils which they supposed to hang over them by Your reign, they turned against You to Your death. "They imagined a device, which they were not able to establish" [Psalm 21:11]. They imagined a device, saying, "It is expedient that one die for all:" [John 11:50] which they were not able to establish, not knowing what they said.

[AD 585] Cassiodorus on Psalms 21:11
To divert evils that loom over some people, we mean to push them aside to another place where there is no iniquity to punish. This is exactly what happened with the suffering of the Lord. For when the Jews believed that Roman power would be a threat to them if they had accepted the Lord Savior as King, it seemed right to them to divert those evils upon him which they believed would befall them when the Romans took up the role of avengers. “They came up with a plan” saying, “It is expedient that one man die for all.” “But this they were not able to establish,” that is, to complete according to their vow. For without knowing it, they spoke the truth. It was necessary that one should die for all. The truth was indeed uttered, but with an evil vow. Therefore they will suffer punishment for such a deed, because they did not have a pure conscience.

[AD 397] Ambrose of Milan on Psalms 21:12
“Turned away” [is] an expression properly applied to the sinner, for “Cain went out from the face of the Lord,” and the psalmist says, “You will make them turn their back.” One who is righteous does not turn away from the Lord but runs to meet him and says, “My eyes are ever toward the Lord.” And when the Lord said, “Whom shall I send?” Isaiah offered himself of his own accord and said, “Behold, here I am.”

[AD 430] Augustine of Hippo on Psalms 21:12
"For You shall set them low." For You shall rank them among those from whom in degradation and contempt You will turn away. "In Your leavings You shall make ready their countenance" [Psalm 21:12]. And in these things that Thou leavest, that is, in the desires of an earthly kingdom, You shall make ready their shamelessness for Your passion.

[AD 390] Diodorus of Tarsus on Psalms 21:13
Exalted though you are, then, you are shown to be more exalted through your power and in outdoing all the arrogant, as by inflicting the blow on them from on high. For this reason we shall not cease singing your praises always.

[AD 430] Augustine of Hippo on Psalms 21:13
"Be Thou exalted, O Lord, in Your strength" [Psalm 21:13]. Be Thou, Lord, whom in humiliation they did not discern, exalted in Your strength, which they thought weakness. "We will sing and praise Your power." In heart and in deed we will celebrate and make known Your marvels.

[AD 458] Theodoret of Cyrus on Psalms 21:13
Not for being lowly is God exalted, nor does he receive what he does not possess; instead, what he possesses he reveals … your exaltation is revealed in your ineffable power, which we shall continue to celebrate and sing, recounting your marvelous works.

[AD 585] Cassiodorus on Psalms 21:13
To sing means to proclaim the words of the Lord with the mouth. To make music on the harp means to fulfill the divine commands faithfully through good works.