Musar zu Ijow 2:6

And a person is obligated to reflect and know that the troubles that find him and the afflictions that come upon him are not according to the greatness of his iniquity and the multitude of his sins. Rather God, may He be blessed - in His pity upon him - afflicts him in the way of the rebuke of a father upon his son, as it is stated (Deuteronomy 8:5), “And you shall know in your heart, that, as a man chastens his son, so the Lord, your God, chastens you.” And our Rabbis, may their memory be blessed, explained (Yalkut Shimoni on Torah 350), “Your heart knows the deeds you have done and the afflictions I have brought upon you; that it is not according to your deeds that I have afflicted you.” And it is stated (Job 11:6), “and know that God has overlooked for you some of your iniquity.” And it is stated (Ezra 9:13), “though You, our God, have been forbearing, [punishing us] less than our iniquity.”
But when reproof comes upon the enemies of the Lord, may He be blessed, they are finished with one iniquity - for the punishment comes all at once, as it is stated (Psalms 34:22), “One misfortune is the deathblow of the wicked.“ So the rest of their iniquities remain upon their souls, as it is stated (Ezekiel 32:27), “and their iniquities shall be upon their bones.” However when reproof comes to the righteous, it comes little by little, until the termination of their iniquities, as it is stated (Amos 3:2), “You alone have I known from all the families of the earth; that is why I will call you to account for all your iniquities.” And our Rabbis, may their memory be blessed, explained (Avodah Zarah 4a), “It is comparable to a person who lends money to two people, one of whom is his friend, and the other one is his enemy. [In the case of] his friend, he collects from him little by little; [whereas in the case of] his enemy, he collects from him all at once.” And it is stated (Proverbs 24:16), “Seven times the righteous man falls and gets up, while the wicked are tripped by one misfortune.” Its explanation is that they stumble upon one misfortune and are finished. And it is stated (Jeremiah 10:24), “Chastise me, O Lord, but only in judgement; not in Your wrath, lest You reduce me to naught.” Its explanation is, “but only in judgement”- with the trait of mercy and and the property of Your kindness. [This is] from the usage (in Numbers 29:18), “in their count according to [their] judgement,” [which means] according to [their] property; [and in] (Psalms 112:5), “who conducts his affairs in justice,” [means] with measure. And they compared it to another parable regarding this matter and said (Midrash Tehillim 18), “One who does not know [how] to hit will hit his son in his eyes and in his face; whereas one who knows [how] to hit will hit his son in such a way that it will not cause him damage.” And likewise is it written (Psalms 118:18), “The Lord surely chastised me, but He did not give me over to death.” And it is stated (Job 2:6), “but only spare his life.”
And He only brings vengeful afflictions upon the evildoers. But probing afflictions only come upon the righteous; for they accept them with love and they increase the refinement of their actions. So [these] afflictions are for their good and their benefit, and the increase of their reward - as it is stated (Psalms 11:5), “The Lord probes the righteous one.” And our Rabbis, may their memory be blessed, compared it to a parable regarding this and said (Bereishit Rabbah 58:32), “When the owner of the flax knows that the flax is strong, he hits it much in order to make it soft and good.”