Deuteronomy 4:30

30.When thou art in tribulation. He here shews the advantage of punishments, on the ground of their usefulness and profit; for what the Apostle says is confirmed by experience, that

“no chastening for the present seemeth to be joyous, but grievous; nevertheless afterward it yieldeth the peaceable fruit of righteousness to them that are exercised thereby.”
(Hebrews 12:11.)

Lest, therefore, they should be provoked to wrath by God’s stripes, he reminds them of their usefulness to them, because they would never turn to God unless aided by this remedy. He tells them that, after they shall have been afflicted by the curses of God, if they sought after Him, they should find Him: and further, he gives them grounds for hope both in God’s nature and in His covenant. He assures them that God will be willing to be appeased, because He is by nature merciful; but he adds another confirmation of this, which is more certain and familiar, viz., because God had adopted them by a perpetual covenant.