Exod 20:6

“and He keeps (stores up) the mercy which a person does to give a reward for it to the thousand generations of that person’s descendants. It follows, therefore, that the measure of good (reward) is greater than the measure of punishment in the proportion of one to five hundred, for the former is threatened only to four generations whilst the latter is bestowed upon thousands (two thousands at least) (Tosefta Sotah 4:1; see Rashi on Exodus 34:7).”

“AND HE SHOWETH MERCY UNTO THE THOUSANDTH GENERATION OF THEM THAT LOVE ME AND KEEP MY COMMANDMENTS. It appears from the sense of the verse that this Divine assurance is with respect to the subject-matter of the commandments that He mentioned. He is thus saying that to those that love Him, He will show mercy to their thousandth generation. These are the ones who sacrifice their lives for Him, for they are the ones who acknowledge only the Glorious Name and His G-dship and deny all strange gods, refusing to worship them even if they are in mortal danger. They are called “the lovers [of G-d],” for this is the kind of love that we have been obligated to observe even at the sacrifice of life, just as He has said, And thou shalt love the Eternal thy G-d with all thy heart, and with all thy soul, and with all thy might, meaning that you should give your very life because of your love of Him, that you should not alter Him for another god, nor join Him together with a strange god. It is for this reason that [the prophet] said of Abraham, the seed of Abraham my friend, since he risked his life in order not to worship the idols in Ur of the Chaldees. The rest of the righteous are called those that keep My commandments. Now many scholars have explained that “His lovers” are those who worship Him without the intention of receiving a reward, just as our Sages have mentioned. But I have found in the Mechilta that it is said: “Of them that love Me. This refers to Abraham and those like him. And those that keep My commandments. This refers to the prophets and the elders. Rabbi Nathan says that the verse, of them that love Me and keep My commandments, refers to those who dwell in the Land of Israel and give their lives for the commandments. ‘Why are you being led out to be executed?’ ‘Because I have circumcised my son.’ ‘Why are you being led out to be burned?’ ‘Because I read the Torah.’ ‘Why are you being led out to be hanged?’ ‘Because I ate the unleavened bread.’ ‘Why are you being lashed with the whip?’ ‘Because I took the lulav.’ And it says, Those with which I was wounded in the house of my friends. These are the wounds which have caused me to become beloved of My Father in heaven.” Thus Rabbi Nathan explained that the love [of G-d, which is referred to in the verse before us], meant the sacrifice of life for the sake of the commandments. Now the verse here certainly refers to idolatry, for it is with reference to it that we are obligated at all times forever to suffer death rather than transgress [the law]. But [Rabbi Nathan] broadened the matter to include all the commandments, [such as circumcision, the study of Torah, the eating of unleavened bread on Passover, the taking of the lulav on Succoth — as mentioned above] — because in the time of religious persecutions, we are obligated to suffer death for any of the commandments [rather than transgress them], as derived from the other verse, And ye shall not profane My holy Name. And it would also be incorrect to say of the first Sage [in the above Mechilta] — i.e., who said that [those who love Me] refers to Abraham, while [those who keep My commandments] refers to the prophets — that he is of the opinion that the prophets kept the commandments with the intention that they receive a reward! [Thus the explanation of “the many scholars” mentioned above is refuted by the Mechilta.] However, there is a secret in this [Mechilta]: Abraham risked his life in love — something like it is written, mercy to Abraham — and the rest of the prophets in g’vurah (might). Understand this.”

“Together with fear one must also love him, because he says of himself: And showing mercy unto thousands to those who love me; in which he shows us that the mercy and kindness of God transcends the punishment of iniquities. When the heart is enlarged through love, then man easily keeps the commandments of God. I have run the way of thy commandments, when thou didst enlarge my heart. I have seen an end of all perfection; thy commandment is exceedingly broad. He says that the way of God's commandments is broad, yet to some it seems to be narrow. Certainly to those who love, it is broad; but to those who do not love, it seems to be narrow.”