Sforno on Exodus 34:7/ספורנו על שמות ל״ד:ז׳

1נוצר חסד לאלפים, He preserves the accumulated merits of the fathers and will let the children draw on these merits.

2נושא עון, premeditated sin.

3ופשע, sins intended to challenge G’d.

4וחטאה, additional to the taunting sin called פשע. We encounter an illustration of this in Jeremiah 11,15 כי רעתכי אז תעלוזי, “for you exult while performing your evil deeds.” We must remember that the degree of evil committed by different people is never a duplicate, i.e. each one commits evil according to his own agenda; hence G’d’s reaction to such evil varies after taking into consideration all the circumstances. This is why all these attributes have been enumerated separately.

5ונקה, even though G’d wipes the slate clean for those penitents motivated by their love for G’d and not by their fear of punishment, לא ינקה, He will not do this for the ones whose only motivation for turning penitent is their fear of G’d’s retribution, or their desire to arrest such retribution. We find confirmation of this in Yuma 86 that i.e. intentional sins of such penitents will be treated as if they had been unintentionally committed sins, a conclusion based on Hoseah 14,2 כי כשלת בעונך, “for you have fallen because of your sin.”

6פוקד עון אבות על בנים, He delays punishing the wicked in the land until their measure of sin is such that they deserve to be wiped out. This “measure” is one that in G’d’s opinion, precludes their ever becoming penitents. (compare Sotah 9). Such a situation usually is not reached until several successive generations are steeped in sin.

7על שלשים, when the latest generation intensifies the evil perpetrated by their fathers and grandfathers. Jeremiah 7,26 describes such a scenario when he writes: “they would not listen to Me or give ear. They stiffened their necks, they acted worse than their fathers.”

8ועל רבעים, when the generations do not become worse than their fathers but commit sins of the same type and seriousness.