Psalms 78:5-8

5. He established a testimony in Jacob. As the reception or approbation of any doctrine by men would not be a sufficient reason for yielding a firm assent to its truth, the prophet proceeds farther, and represents God as the author of what he brings forward. He declares, that the father’s were not led to instruct their children in these truths under the mere impulse of their own minds, but by the commandment of God. Some understand the words, He hath established a testimony in Jacob, and appointed a law in Israel, as implying that God had established a decree in Jacob, to be observed as an inviolable rule, which was, that the deliverance divinely wrought for the people should be at all times in the mouth of every Israelite; but this seems to give too restricted a sense. I therefore consider statute, or testimony, and law, as referring to the written law, which, however, was partly given for this end, that by the remembrance of their deliverance, the people, after having been once gathered into one body, might be kept in their allegiance to God. The meaning then is, that God not only acquired a right to the Jews as his people by his mighty power, but that he also sealed up his grace, that the knowledge of it might never be obliterated. And, undoubtedly, it was then registered as it were in public records, when the covenant was ratified by the written law, in order to assure the posterity of Abraham that they had been separated from all other nations. It would have been a matter of very small importance to have been acquainted with, or to have remembered the bare history of what had been done, had their eyes not been, at the same time, directed to the free adoption and the fruit of it. The decree then is this, That the fathers being instructed in the doctrine of the law themselves, should recount, as it were, from the mouth of God, to their children, that they had been not only once delivered, but also gathered into one body as his Church, that throughout all ages they might yield a holy and pure obedience to him as their deliverer. The reading of the beginning of the second clause of the verse properly is, Which he commanded, etc. But the relative אשר, asher, which, I have no doubt, is here put by way of exposition for namely, or that is, he commanded, etc. I have translated it for, which amounts to the same thing.