Albert Barnes Commentary Psalms 37:1

"Fret not thyself because of evil-doers, Neither be thou envious against them that work unrighteousness." — Psalms 37:1 (ASV)

Fret not yourself - The Hebrew word here means properly to burn, to be kindled, to be inflamed, and is often applied to anger, as if under its influence we become “heated”: (Genesis 31:36; Genesis 34:7; 1 Samuel 15:11; 2 Samuel 19:43). Hence, it means to fret oneself, to be angry, or indignant. . We should perhaps express the same idea by the word “worrying” or “chafing.” The state of mind is that where we are worried, or envious, because others are prosperous and successful, and we are not. The idea is, therefore, closely allied with that in the other part of the verse, neither be you envious.

Because of evildoers - Wicked men:

• At the fact that there are wicked men, or that God allows them to live;
• At their numbers;
• At their success and prosperity.

Neither be you envious - Envy is pain, mortification, discontent, at the superior excellence or prosperity of others, accompanied often with some degree of malignant feeling, and with a disposition to detract from their merit. It is the result of a comparison of ourselves with others who are more highly gifted or favored, or who are more successful than we are ourselves. The feeling referred to here is that which springs up in the mind when we see persons of corrupt or wicked character prospered, while we, endeavoring to do right, are left to poverty, to disappointment, and to tears.