Albert Barnes Commentary Psalms 19:11

"Moreover by them is thy servant warned: In keeping them there is great reward." — Psalms 19:11 (ASV)

Moreover by them is thy servant warned—The word used here, זהר (zâhar), means, properly, to be bright, to shine; then, to cause to shine, to make light; and then, to admonish, to instruct, to warn. The essential idea here is to throw light on a subject, so as to show it clearly—that is, to make the duty plain and the consequences plain. Compare Leviticus 15:31; Ezekiel 3:18; Ezekiel 33:7. The word is rendered admonished in Ecclesiastes 4:13 and Ecclesiastes 12:12; warn and warned in Psalm 19:11, 2 Kings 6:10, 2 Chronicles 19:10, Ezekiel 3:17–21, and Ezekiel 33:3-9; teach in Exodus 18:20; and shine in Daniel 12:3. It does not occur elsewhere.

And in keeping of them there is great reward—Either as the result of keeping them, or in the act of keeping them. In the former sense, it would mean that a careful observance of the laws of God will be followed by rewards hereafter; in the other sense, that the act of keeping them will be attended with so much peace and happiness as to constitute of itself an ample reward. In both these senses is the assertion here made a correct one. Both will be found to be true.

It is not easy to determine which is the true sense. Perhaps the language implies both. The phrase thy servant refers to the author of the psalm. It shows that in this part of the psalm—when speaking of the “sweetness” of the law of God, of its value as perceived by the soul, and of the effect of keeping that law—he is referring to his own experience.