Thou hast put gladness in my heart. David is an example to the de-spending ones. Notwithstanding his sufferings and calamities, God has looked on him, and so "put gladness in his heart"—a gladness which far exceeds that of his adversaries.
Though they are in prosperity, and have their corn and wine increased, and enjoy all the "outward material blessings promised to Israel—the wheat and the grape—for a supply of which he is indebted to the generosity of friends" (Kay), yet he would not change places with them.
The spiritual joy which fills his own heart is preferable to any amount of material comforts and pleasures.