Psalms 37:4

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, (21) as we have seen in Psalms 16:5. 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 favor 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.