Albert Barnes Commentary Psalms 37:3

"Trust in Jehovah, and do good; Dwell in the land, and feed on [his] faithfulness." — Psalms 37:3 (ASV)

Trust in the Lord - Confide in him; rest on him. Instead of allowing the mind to be disturbed and sad because there are wicked men upon the earth; because they are prosperous and apparently happy; because they may injure you in your person or reputation (Psalms 37:6), calmly confide in God. Leave all this in his hands. Feel that he rules, and that what he permits is wisely permitted; and that whatever may occur, it will all be overruled for his own glory and the good of the universe.

And do good - Always be engaged in some work of benevolence.

• If there are wicked men in the world, if wickedness abounds around us, there is all the more reason for us to endeavor to do good. If others are doing evil, we should do good; if they are wicked, we cannot do a better work than to do good to them, for the best way of meeting the wickedness of the world is to do it good.
• The best way to keep the mind from complaining, chafing, and fretting is to always be engaged in doing good; to have the mind always occupied with something valuable and useful. Each one should have so much of his own to do that he will have no time to murmur and complain, to allow the mind to prey on itself, or to “corrode” for lack of employment.

So shalt thou dwell in the land - This would be more correctly translated as a command: “Dwell in the land.” That is, abide safely or securely in the land - referring, perhaps, to “the land” as the land of promise—the country given to the people of God. The idea is that they should abide there calmly and securely; that they should not worry themselves because there were wicked men upon the earth and because they were successful, but that they should be thankful for their inheritance and partake gratefully of the bounties which they receive from the hand of God. .

And verily thou shalt be fed - Margin, “in truth or stableness.” The “literal” meaning would be, “Feed on truth.” The word rendered “fed” is here in the imperative mood. It properly means to feed, as a flock, and then to feed upon anything in the sense of delighting in or taking pleasure in anything, as if we found our support or sustenance in it. And here it means, doubtless, “Feed on truth”; that is, seek after truth, find delight in it, and let it be the food of your souls. The word here rendered “verily” means, as in the margin, “truth,” and the meaning is that they should seek after truth and find their support and comfort in that.

There are, then, in this verse, four things prescribed as duty, in order to keep the mind calm in view of the fact that wickedness abounds in the world:

1. to confide in God;
2. to be actively employed in doing good;
3. to abide calmly and gratefully in the land which God has given us;
4. to seek after truth, or a true view of the character and government of God as the great Ruler.

If people would do these things, there would be little complaining and fretting in the world.