John Calvin Commentary Psalms 78:5

"For he established a testimony in Jacob, And appointed a law in Israel, Which he commanded our fathers, That they should make them known to their children;" — Psalms 78:5 (ASV)

He established a testimony in Jacob. As the reception or approval of any doctrine by men would not be a sufficient reason for yielding a firm assent to its truth, the prophet proceeds further and represents God as the author of what he brings forward. He declares that the fathers 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: that the deliverance divinely wrought for the people should be at all times in the mouth of every Israelite. However, this seems to give too restricted a sense.

I therefore consider statute, or testimony, and law as referring to the written law. This law, however, was partly given for this purpose: 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 he also sealed up his grace so 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. Merely being acquainted with, or remembering the bare history of what had been done, would have been of very small importance if their eyes had not, at the same time, been directed to the free adoption and its fruit.

The decree, then, is this: that the fathers, being instructed in the doctrine of the law themselves, should recount to their children, as it were from the mouth of God, that they had not only been delivered once but also gathered into one body as his Church, so 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 pronoun אשר (asher), which is 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.