Charles Ellicott 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)

For he ... —Better, taking the relative of time (Psalms 139:15), For he established (it as) a testimony in Jacob and (as) a law appointed (it) in Israel when he commanded our forefathers to make them (the “wonderful works” of last verse) known to their children. For the custom see reference in margin.