Albert Barnes Commentary Psalms 37:4

"Delight thyself also in Jehovah; And he will give thee the desires of thy heart." — Psalms 37:4 (ASV)

Delight yourself also in the - Lord. The word rendered “delight” means properly to live delicately and effeminately; then, to be tender or delicate; then, to live a life of ease or pleasure; then, to find delight or pleasure in anything. The meaning here is, that we should seek our happiness in God - in His being, His perfections, His friendship, His love.

And He shall give you the desires of your heart - literally, the “askings,” or the “requests” of your heart. What you really “desire” will be granted to you. That is:

1. the fact that you seek your happiness in Him will regulate your desires, so that you will be “disposed” to ask only those things which it will be proper for Him to grant; and
2. the fact that you do find your happiness in Him will be a reason why He will grant your desires.

The fact that a child loves his father, and finds his happiness in doing his will, will do much to regulate his own “wishes” or “desires,” and will at the same time be a reason why the father will be disposed to comply with his requests.