Psalms 78:4,5

Showing the praises of the Lord His glorious and praiseworthy actions, as the following words explain it. For he established a testimony in Jacob That is, his law, as it is called in the next clause; which is very often termed a testimony, because it is a witness between God and men, declaring both the duties which God expects from man, and the promises and blessings which man, in the performance of his duty, may expect from God. This is justly put in the first place as the chief of all the following mercies, and the foundation of their temporal and spiritual prosperity. Which he commanded, &c. Which testimony, or law, God revealed to them, not for their own private use merely or chiefly, but for the benefit of all their posterity, to whom their parents were obliged to teach it, and who were required to hear, read, and study it.