20 “How great” is “the multitude of Your sweetness, O Lord”. Here the Prophet exclaims, having sight of all this, and admiring how manifoldly plenteous is Your sweetness, O Lord. “Which You have hid for them that fear You.” Even those, whom Thou correctest, You love much: but lest they should go on negligently from relaxed security, Thou hidest from them the sweetness of Your love, for whom it is profitable to fear You. “You have perfected it for them that hope in You.” But You have perfected this sweetness for them that hope in You. For Thou dost not withdraw from them what they look for perseveringly even unto the end. “In sight of the sons of men.” For it does not escape the notice of the sons of men, who now live no more after Adam, but after the Son of Man. “You will hide them in the hidden place of Your Countenance:” which seat You shall preserve for everlasting in the hidden place of the knowledge of You for them that hope in You. “From the troubling of men.” So that now they suffer no more trouble from men.
21. “You will protect them in Your tabernacle from the contradiction of tongues”. But here meanwhile while evil tongues murmur against them, saying, Who has come thence? You will protect them in the tabernacle, that of faith in those things, which the Lord wrought and endured for us in time.
22. “Blessed be the Lord; for He has made His mercy marvellous, in the city of compassing”. Blessed be the Lord, for after the correction of the sharpest persecutions He has made His mercy marvellous to all throughout the world, in the circuit of human society.
23. “I said in my ecstasy”. Whence that people again speaking says, I said in my fear, when the heathen were raging horribly against me. “I have been cast forth from the sight of Your eyes.” For if You had regard to me, You would not suffer me to endure these things. “Therefore You heard, O Lord, the voice of my prayer, when I cried unto You.” Therefore putting a limit to correction, and showing that I have part in Your care, You heard, O Lord, the voice of my prayer, when I raised it high out of tribulation.
24. “Love the Lord, all you His saints”. The Prophet again exhorts, having sight of these things, and says, “Love the Lord, all you His saints; for the Lord will require truth.” Since “if the righteous shall scarcely be saved, where shall the sinner and the ungodly appear?” “And He will repay them that do exceeding proudly.” And He will repay them who even when conquered are not converted, because they are very proud.
25. “Quit you like men, and let your heart be strengthened”: working good without fainting, that you may reap in due season. “All you who trust in the Lord:” that is, you who duly fear and worship Him, trust ye in the Lord.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)