Adam Clarke on Psalms 78:38

But he, being full of compassion - Feeling for them as a father for his children.

Forgave their iniquity - יחפר yechapper, made an atonement for their iniquity.

And did not stir up all his wrath - Though they often grieved his Spirit, and rebelled against him, yet he seldom punished them; and when he did chastise them, it was as a tender and merciful Father. He did not stir up all his wrath - the punishment was much less than the iniquity deserved.