Sforno on Deuteronomy 7:12/ספורנו על דברים ז׳:י״ב

1והיה 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.]

2את המשפטים, for the earth’s continued existence is linked to performance of justice by its inhabitants. (Proverbs 29,4)

3ושמרתם, and study them, (according to Sifri)

4ועשיתם אותם, as a result of studying them you will perform them in accordance with halachah.

5ושמר 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.]

6ואת 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.)