Deuteronomy 7:12

If you receive these judgments, and observe and perform them, then will the Lord your God keep with you the covenant and the lovingkindness which He sware to your fathers.

consequently i.e., the end reward — as in, “always, to the end” [Psalms 119: 112]. The meaning of the earlier passage “He keeps the covenant” [: 9] is that he kept the covenant of Abraham; but if you are among “those that love him” [: 9], then He will continue to keep the covenant. If you are one of “those who love him”, then He will love you, and bless you, and increase you (this being the meaning of “the covenant and the kindness” [: 9]).

AND IT SHALL COME TO PASS ‘EIKEV’ YE HEARKEN. Eikev means “because.” So also, ‘eikev’ (because) that Abraham hearkened to My voice. And Rashi wrote: “If you will hearken even to the lighter commandments which a person usually treads upon with his ‘heels’ [i.e., those commandments which a person is inclined to treat lightly] then G-d will keep His promise to you.” as meaning “heel, footprint.” — The term “lighter commandments” thus means “lighter” in the sense that people regard them lightly because they think that the reward for their observance is of minor significance, and therefore, “they tread upon them with their heels,” so to say. But, as Scripture continues, these people are mistaken, since the reward for even these commandments is boundless. Now Scripture mentions the ordinances [And it shall come to pass ‘eikev’ ye hearken to these ‘ordinances’] mentioned here? It must be that the sense of the verse is as follows: “If you will hearken to those commandments which a person is inclined to treat lightly, such as the ordinances about monetary matters — then etc.” Thus, the reason ordinances are singled out more than statutes and testimonies is that Scripture wants to teach us that we should not hold them in disdain despite the fact that they deal merely with monetary matters. perhaps because he admonishes them not to be disdainful of the lightly-esteemed ordinances such as the laws pertaining to monetary matters.
And the commentators have said that the meaning of the word eikev is that “in the end” there will be reward. Similarly, in keeping them [the ordinances of G-d] ‘eikev rav’ (there is [in the end] great reward). The verse here is thus stating: “and the end [the ultimate consequence] of your hearkening to the ordinances and your observing them is that G-d shall keep the covenant and the mercy, and He will love thee. ” This is correct, for in the Sacred Language the beginning of anything is called rosh [literally: “head”], as it is said, ‘rosh’ (the beginning of) Thy word is truth. So also is the leader of the generation called “the head of the people,” and the best of spices is called rosh. (‘the chief’ spices). Similarly, the conclusion of any matter is called akeiv (heel) as the Sacred Language adopts these figurative expressions from the human body; and thus “the head” is the beginning while “the …

ושמר ה' אלוקיך לך, G’d keeps His covenant, i.e. the assurances He gave to the patriarchs concerning their descendants, with any generation which is fit, loyal and deserving. If the descendants do not keep His commandments then the covenant is valid for subsequent generations which do observe the terms of the covenant.

והיה עקב תשמעון, Moses explains that the reason why the King, i.e. G’d, commands them to observe all these commandments is in order to be able to fulfill the promises made to their forefathers regarding them. The people were meant to observe these commandments out of a feeling of love for G’d, not because they did so in order to earn a reward. [If I understand the author correctly, the wordsואת החסד in the phrase את הברית והחסד, are to establish reciprocity of G’d’s loving care for the patriarchs, the parties to the covenant, and their descendants’ feeling of love on their part towards the Creator. Ed.]

את המשפטים, for the earth’s continued existence is linked to performance of justice by its inhabitants. (Proverbs 29,4)

ושמרתם, and study them, (according to Sifri)

ועשיתם אותם, as a result of studying them you will perform them in accordance with halachah.

ושמר ה' אלוקיך לך את הברית, the one He swore, when He said (Genesis 17,7) “I will give My covenant between Me and you, and between your descendants after you for all generations as an eternal covenant, to be your G’d and that of your descendants after you.” Being our G’d means that He will supervise our fates not by means of some intermediary, such as the fates which are supervised by appointees of G’d, including horoscopes, and angels assigned to each nation. Besides, anything which is done by G’d personally, without His having recourse to an intermediary, is something that endures forever. Compare Kohelet 3,14 כי כל אשר יעשה האלוקים הוא אשר יהיה לעולם,”anything which G’d does Himself is something that will endure forever.” By contrast, transient phenomena, [such as extinct species, for instance, Ed.] are proof of the fact that they were the products of intermediaries of G’d. [G’d had commanded the waters to produce the living creatures of the waters, and He had commanded the earth to produce vegetation and the mammals, etc. Water and the earth are both intermediaries. Ed.]

ואת החסד, as He had said in Genesis 17,8 when He promised the land of Canaan to Avraham’s descendants. Such acts are acts of loving kindness and have nothing to do with the reward awaiting us as compensation for performing the commandments in the world to come. (based on the statement in Kidushin 39 that reward, in the sense of compensation, for commandments performed is not something that is due while we are on earth.)

והיה עקב תשמעון, “it will be as a consequence of your hearkening, etc.” Rashi comments on why Moses used the word עקב, “heel,” here when he could have used numerous other words meaning: “as a result of.” He says that Moses refers here to the kind of commandments which the average person tramples underfoot with his heel, is hardly conscious of, for the observance of which meticulously the Torah promises great reward, even though it takes no effort to fulfill theses commandments. This is also what David had in mind in Psalms 49,6 when he said: למה אירא רע בימי עון עקבי יסובני, “why should I be afraid of trouble in days to come –seeing that I have fulfilled the most difficult commandments?-He answers rhetorically, “I have reason to be afraid of being punished for trespassing the commandments that are so easy to fulfill as it is to put one heel behind another.” Our sages in Ethics of the Fathers chapter 2 mishnah 1, warn us to be as meticulous to fulfill the commandments which are easy to fulfill as we are with fulfilling the commandments which are difficult and expensive to fulfill. Something along the same line has been written in Proverbs 5,6 where Solomon warns: ארח חיים פן תפלס נעו מעגלותיה לא תדע “she (the immoral woman who is the subject here) does not chart a path of life; her ways are unstable; you do not know them.” Solomon warns us not to apply our yardsticks to different commandments and taking credit for the ones we performed with a great deal of effort, while neglecting to fulfill the ones we considered as unimportant. We have no way of knowing how G–d values the performance of different commandments, so that we do not know what rewards are in store for their performance. This can be illustrated best by a parable. A king had an orchard; he brought workmen to that orchard to plant trees and did not tell them how much he would pay each for each tree that they planted. If he had told them beforehand which planting would be paid for most, he would find at the end that only half the orchard had been planted with trees, as the workers would, of course, all plant the trees for which they would be paid the most. According to Rabbi Shimon ben Yochai, G–d revealed the reward of only two of all the commandments; one is the commandment which is the easiest to fulfill, the other is the commandment which is the hardest to fulfill. Honouring father and mother is the easiest commandment to fulfill, it can be fulfilled several times daily without special effort. The other is the sending away of the mother bird when one plans to take the chicks it had hatched or was about to hatch. Both of these commandments are rewarded with same reward, long life of the person who fulfills them. The reason is that G–d wanted to show the world that there are commandments which we think must carry a great reward, and others which precisely because they are so easy to fulfill, and the opportunity to fulfill them is ever present, so that we might have thought that they cannot carry much of a reward. [The author continues with further elaborations, which I have omitted as the point has been made sufficiently. Ed.]