Charles H. Spurgeon on Psalms 78:38

But he, being full of compassion, forgave their iniquity, and destroyed them not. Though they were full of flattery, he was full of mercy, and for this cause he had pity on them. Not because of their pitiful and hypocritical pretensions to penitence, but because of his own real compassion for them he overlooked their provocations. Yea, many a time turned he his anger away. When he had grown angry with them he withdrew his displeasure. Even unto seventy times seven did he forgive their offences. He was slow, very slow, to anger. The sword was uplifted and flashed in midair, but it was sheathed again, and the nation yet lived. Though not mentioned in the text, we know from the history that a mediator interposed, the man Moses stood in the gap; even so at this hour the Lord Jesus pleads for sinners, and averts the divine wrath. Many a barren tree is left standing because the dresser of the vineyard cries, "let it alone this year also." And did not stir up all his wrath. Had he done so they must have perished in a moment. When his wrath is kindled but a little men are burned up as chaff; but were he to let loose his indignation, the solid earth itself would melt, and hell would engulf every rebel. Who knoweth the power of thine anger, O Lord? We see the fulness of God's compassion, but we never see all his wrath.