Psalms 73:3

I was envious at the foolish - I saw persons who worshipped not the true God, and others who were abandoned to all vices, in possession of every temporal comfort, while the godly were in straits, difficulties, and affliction. I began then to doubt whether there was a wise providence; and my mind became irritated. It seems to have been a maxim among the ancient heathens, Θεου ονειδος τους κακους ευδαιμονειν, "The prosperity of the wicked is a reproach to the gods." But they had no just conception of a state of future rewards and punishments. Besides, man could not bear prosperity. If men had uninterrupted comforts here, perhaps not one soul would ever seek a preparation for heaven. Human trials and afflictions, the general warfare of human life, are the highest proof of a providence as benevolent as it is wise. Were the state of human affairs different from what it is, hell would be more thickly peopled; and there would be fewer inhabitants in glory. There is reason to doubt whether there would be any religion upon earth had we nothing but temporal prosperity. Indeed, all the following verses are proofs of it.

For I was envious at the foolish - The word "foolish" here refers to sinners. It may either refer to them as foolish, or as proud, insolent, vain - for so the word is elsewhere used. See Psalm 14:1.

When I saw the prosperity of the wicked - More literally, "the peace of the wicked." The reference is not so much to their prosperity in general as to their peace; their conscious safety; their freedom from trouble; and especially their calmness, and their freedom from suffering, in death. From all this he was led for the moment to doubt whether there was any advantage in religion; whether God was just; and whether he befriended the righteous anymore than he did the wicked.