Or HaChaim on Exodus 20:6/אור החיים על שמות כ׳:ו׳

1 ועשה חסד לאלפים, "and Who performs deeds of loving kindness even to thousands." The main point is that even when G'd pays a reward He does not pay the entire reward in one generation but chooses the installments of such a reward in such a way that it maximises enjoyment of it over many generations. In a certain sense the reward is a form of protection against harmful experiences in store for subsequent generations. Shemot Rabbah 44,3 explains that if G'd had paid all the reward that Abraham was entitled to while he was alive, how (by what merit) would his descendents have been able to secure their livelihood? [how could G'd have found sufficient merit to forgive their descendants the sin of the golden calf? Ed.]

2ולשומרי מצותיו, and to those who observe His commandments. According to Sotah 31 these words are not connected with the words "to thousands of generations." People who serve the Lord because they are afraid of punishment cannot expect subsequent generations to draw on their unexpired portion of reward for longer than one thousand generations, whereas the unexpired portion of the reward of people who served the Lord because of love for Him may remain valid for up to two thousand generations. The Talmud derives this from Deut. 7,9 where the Torah speaks about a reward extending for one thousand generations.