4. And delight thyself in Jehovah. This delight is set in opposition to the vain and deceitful allurements of the world, which so intoxicate the ungodly, that despising the blessing of God, they dream of no other happiness than what presents itself for the time before their eyes. This contrast between the vain and fickle joys with which the world is deluded, and the true repose enjoyed by the godly, ought to be carefully observed; for whether all things smile upon us, or whether the Lord exercise us with adversities, we ought always to hold fast this principle, that as the Lord is the portion of our inheritance, our lot has fallen in pleasant places, as we have seen in Psalm 16:5, 6. We must therefore constantly recall to our minds this truth, that it can never be well with us except in so far as God is gracious to us, so that the joy we derive from his paternal favour towards us may surpass all the pleasures of the world. To this injunction a promise is added, that, if we are satisfied in the enjoyment of God alone, he will liberally bestow upon us all that we shall desire: He will give thee the desires of thy heart. This does not imply that the godly immediately obtain whatever their fancy may suggest to them; nor would it be for their profit that God should grant them all their vain desires. The meaning simply is, that if we stay our minds wholly upon God, instead of allowing our imaginations like others to roam after idle and frivolous fancies, all other things will be bestowed upon us in due season.
Ver. 4.—Delight thyself also in the Lord. Draw from communion with God all that inward intensity of joy which it is capable of giving. And he shall give thee the desires of thine heart. God will then grant thee all thy desires, and make thee perfectly happy.
4. desires—(Ps 20:5; 21:2), what is lawful and right, really good (Ps 84:11).
4. There is an ascent in this third precept. He who was first bidden not to fret, was then commanded actively to trust, and now is told with holy desire to delight in God. “Delight thyself also in the Lord.” Make Jehovah the joy and rejoicing of thy spirit. Bad men delight in carnal objects; do not envy them if they are allowed to take their fill in such vain idols; look thou to thy better delight, and fill thyself to the full with thy sublimer portion. In a certain sense imitate the wicked; they delight in their portion—take care to delight in yours, and so far from envying you will pity them. There is no room for fretting if we remember that God is ours, but there is every incentive to sacred enjoyment of the most elevated and ecstatic kind. Every name, attribute, word, or deed of Jehovah, should be delightful to us, and in meditating thereon our soul should be as glad as is the epicure who feeds delicately with a profound relish for his dainties. “And he shall give thee the desires of thine heart.” A pleasant duty is here rewarded with another pleasure. Men who delight in God desire or ask for nothing but what will please God; hence it is safe to give them carte blanche. Their will is subdued to God’s will, and now they may have what they will. Our innermost desires are here meant, not our casual wishes; there are many things which nature might desire which grace would never permit us to ask for; these deep, prayerful, asking desires are those to which the promise is made.
37:4 But suppose you have had great desires to carry on a certain ministry for the Lord. You feel confident that He has been leading you, and your only desire is to glorify Him. Yet a powerful adversary has opposed, blocked, and thwarted you at every bend in the road. What do you do in a case like this? The answer is that you delight yourself also in the Lord, knowing that in His own time He shall give you the desires of your heart. It is not necessary for you to fight back. “The battle is not yours, but God’s” (2 Chron. 20:15). “The Lord will fight for you, and you shall hold your peace” (Ex. 14:14).
 Jamieson, R., Fausset, A. R., & Brown, D. (1997). Commentary Critical and Explanatory on the Whole Bible (Vol. 1, p. 358). Oak Harbor, WA: Logos Research Systems, Inc.
 MacDonald, W. (1995). Believer’s Bible Commentary: Old and New Testaments. (A. Farstad, Ed.) (p. 603). Nashville: Thomas Nelson.