He will not always chide David, from the attributes ascribed to God in the preceding verse, draws the conclusion, that when God has been offended, he will not be irreconcilable, since, from his nature, he is always inclined to forgive. It was necessary to add this statement; for our sins would be continually shutting the gate against his goodness were there not some way of appeasing his anger. David tacitly intimates that God institutes an action against sinners to lay them low under a true sense of their guilt; and that yet he recedes from it whenever he sees them subdued and humbled. God speaks in a different manner in Genesis 6:3, where he says, "My Spirit shall no longer strive with man," because the wickedness of men being fully proved, it was then time to condemn them. But here David maintains that God will not always chide, because so easy is he to be reconciled, and so ready to pardon, that he does not rigidly exact from us what strict justice might demand. To the same purpose is the language in the second clause: nor will he keep anger for ever The expression, to keep anger for ever, corresponds with the French phrase, Je lui garde, Il me l'a garde, [1] which we use when the man, who cannot forgive the injuries he has received, cherishes secret revenge in his heart, and waits for an opportunity of retaliation. Now David denies that God, after the manner of men, keeps anger on account of the injuries done to him, since he condescends to be reconciled. It is, however, to be understood that this statement does not represent the state of the Divine mind towards all mankind without distinction: it sets forth a special privilege of the Church; for God is expressly called by Moses, (Deuteronomy 5:9) "a terrible avenger, visiting the iniquities of the fathers upon the children." But David, passing by unbelievers, upon whom rests the everlasting and unappeasable wrath of God, teaches us how tenderly he pardons his own children, even as God himself speaks in Isaiah, (Isaiah 54:7, 8,) "For a small moment have I forsaken thee; but with great mercies will I gather thee. In a little wrath I hid my face from them for a moment; but with everlasting kindness will I have mercy on thee."

Footnotes

1 - "I am watching him, as he has watched to do a bad turn to me."

He will not always chide - Rebuke; contend; strive; for so the Hebrew word means. He will not always contend with people, or manifest his displeasure. See the notes at Isaiah 57:16; notes at Psalm 78:38-39. This implies that he may chide or rebuke his people, but that this will not be forever. He will punish them; he will manifest his displeasure at their sins; he will show that he does not approve of their course, but he will show that he "loves them," and does not seek their ruin.
Neither will he keep his anger for ever - The words "his anger" are supplied by the translators, but not improperly. The meaning is the same as in the former member of the sentence. He will not cherish hatred when the object of the chastisement is accomplished. It is not his character to retain anger for its own sake, or for any personal gratification.

He will not always chide - He will not contend with us continually. He has often reproved, often punished us; but his mercy ever rejoiced over judgment.

He will not always (f) chide: neither will he keep [his anger] for ever.
(f) He shows first his severe judgment, but as soon as the sinner is humbled, he receives him to mercy.

He will not always chide,.... He sometimes does chide his children, though never but when they have done a fault; always for their sins, in order to bring them to a sense and acknowledgment of them, and to depart from them; not for chiding sake, as some parents, to gratify their passion and ill humour, who correct for their own pleasure; but the Lord chides and corrects for the profit of his children, that they may be partakers of his holiness; he ever does it for their good, but he will not always chide, or continue it ever: or "he will not always contend" (e), strive with them, litigate a point with them, hold out a controversy, not being able to stand before him; he knows their frame, their weakness, and frailty; see Isaiah 57:16,
neither will he keep his anger for ever; though he does with the wicked, yet not with his own people; that endures but for a moment, and is rather seeming than real; and what does appear is soon turned away; he does not retain it long, he is quickly pacified towards them for all they have done, and smiles again upon them, Micah 7:18.
(e) "contendet", Pagninus, Montanus; "litigat", Junius & Tremellius, Piscator; "litigabit", Vatablus, Gejerus, Michaelis.