Numbers 14:18

Adonoy, slow to anger. At the righteous and at the wicked. When Moshe ascended on high, he found the Holy One, Blessed is He, sitting and writing, “Hashem is slow to anger.” He (Moshe) said to Him, ‘to the righteous’? The Holy One, Blessed is He, said to him, ‘even to the wicked’! He (Moshe) said to Him, ‘let the wicked perish’! He said to him ‘by your life, you will need this thing.’ When the Israelites sinned with the [golden] calf and the spies, Moshe prayed before Him with “slow to anger.” The Holy One, Blessed is He, said: “But you said to Me ‘to the righteous”’? He (Moshe) said to Him: “But You said to me, ‘Even to the wicked’.”

Acquit. Those who repent.

[He] does not acquit. Those who do not repent.

The Lord is long­ suffering, and nigh in mercy, forgiving sins and covering transgressions, justifying such as return to His law though them who turn not He will not absolve, but will visit the sins of wicked fathers upon rebellious children unto the third and fourth generation.

פוקד עון אבות על בנים, this may extend until the fourth generation, i.e. if the fourth generation of the original sinner will still continue in the wicked ways of their forbears that will make the measure of sin of those families in the third generation so full that it has become irreversible and G’d will take the appropriate action. If the sons and grandsons continued in the evil ways of their forbears but not until the fourth generation, G’d will suspend retribution to see how the fourth generation would conduct themselves before exacting retribution.

ונקה לא ינקה, “and He will not let a guilty person be exonerated completely without having paid a price for knowingly having sinned.” [This is the standard explanation of this expression. Ed.] Our author- if I understand him correctly,- understands it as G–d saying that the world we live in will never be completely free of deliberate sinners. He used Jeremiah 30,11 as his proof for this interpretation. The Prophet there says: ויסרתיך למשפט ונקה לא ינקך, (after having wiped out the sinful nations) “but I will not let you go unpunished, but I will chastise you in measure”.

פוקד עון אבות על בנים, “visiting the sins of the fathers on the children;” this is another aspect of G–d’s attribute of Mercy, that He delays punishing the fathers, waiting if the children or grandchildren will return to Him before carrying out the punishment that had been deserved by them. In Exodus 34,7, where the list of G–d’s attributes first appears, the wording isבני בנים , “grandchildren,” not “children,” as here. In both instances, the point G–d makes is that while He may delay exacting punishment, depending on the severity of the sin in question, He will not allow sins that are not repented to go totally unpunished.