John Calvin Commentary Psalms 77:9

"Hath God forgotten to be gracious? Hath he in anger shut up his tender mercies? Selah" — Psalms 77:9 (ASV)

Has God forgotten to be merciful? The prophet still continues debating with himself on the same subject. His object, however, is not to overthrow his faith, but rather to raise it up. He does not ask this question as if the point to which it refers were a doubtful matter.

It is as if he had said, Has God forgotten himself? Or, has he changed his nature? For he cannot be God unless he is merciful. I indeed admit that the prophet did not remain unshaken, as if he had a heart of steel. But the more violently he was assailed, the more firmly did he lean upon the truth that the goodness of God is so inseparably connected with his essence as to make it impossible for him not to be merciful.

Whenever, therefore, doubts enter our minds when we are harassed with cares and oppressed with sorrows, let us learn always to strive to arrive at a satisfactory answer to this question: Has God changed his nature so as to be no longer merciful? The last clause, Has he shut up or restrained his compassions in his anger? is to the same effect.

It was a very common and notable observation among the holy patriarchs that God is longsuffering, slow to wrath, ready to forgive, and easily entreated. It was from them that Habakkuk derived the statement which he makes in his song:

Even in his anger he will be mindful of his mercy (Habakkuk 3:2).

The prophet, then, here comes to the conclusion that the chastisement he felt would not prevent God from being reconciled to him again, and returning to his accustomed manner of bestowing blessings upon him, since his anger towards his own people endures only for a moment.

Indeed, although God manifests the signs of his anger, he does not cease most tenderly to love those whom he chastises. His wrath, it is true, rests continually upon the reprobate. But the prophet, considering himself among the number of God’s children and speaking of other genuine believers, justly argues from the impossibility of God ceasing to be merciful that God's temporary displeasure cannot interrupt the course of his goodness and mercy.