Albert Barnes Commentary Psalms 119:4

"Thou hast commanded [us] thy precepts, That we should observe them diligently." — Psalms 119:4 (ASV)

Thou hast commanded - All this is here traced to the command of God; to the fact that he has required it. It is not mere human prudence; it is not mere morality; it is not because it will be for our interest; it is because God requires it. This is the foundation of all true virtue; and until a man acts from this motive, it cannot be said that he is in the proper sense a righteous man.

To keep thy precepts diligently - Hebrew, “very much;” that is, to do it constantly, faithfully. Each one of his laws is to be observed, and to be observed always, and in all circumstances.