2 This it is that disturbs you who are a Christian; that you see men of bad lives prospering, and surrounded with abundance of things like these; you see them sound in health, distinguished with proud honours; you see their family unvisited by misfortune; the happiness of their relatives, the obsequious attendance of their dependants, their most commanding influence, their life uninterrupted by any sad event; you see their characters most profligate, their external resources most affluent; and your heart says that there is no Divine judgment; that all things are carried to and fro by accidents, and blown about in disorderly and irregular motions. For if God, you say, regarded human affairs, would his iniquity flourish, and my innocence suffer? Every sickness of the soul has in Scripture its proper remedy. Let him then whose sickness is of that kind that he says in his heart things like these, let him drink this Psalm by way of potion....
3. “Be not envious because of evil-doers, neither be envious against the workers of iniquity”. “For they shall soon wither like the grass, and shall fade like the herbs of the meadow”. That which to you seems long, is “soon” in the sight of God. Conform you yourself to God; and it will be “soon” to you. That which he here calls “grass,” that we understand by the “herbs of the meadow.” They are some worthless things, occupying the surface only of the ground, they have no depth of root. In the winter then they are green; but when the summer sun shall begin to scorch, they will wither away. For now it is the season of winter. Your glory does not as yet appear. But if your love has but a deep root, like that of many trees during winter, the frost passes away, the summer (that is, the Day of Judgment) will come; then will the greenness of the grass wither away. Then will the glory of the trees appear. “For you” (says the Apostle) “are dead,” even as trees seem to be in winter, as it were dead, as it were withered. What is our hope then, if we are dead? The root is within; where our root is, there is our life also, for there our love is fixed. “And your life is hid with Christ in God.” When shall he wither who is thus rooted? But when will our spring be? When our summer? When will the honour of foliage clothe us around, and the fullness of fruit make us rich? When shall this come to pass? Hear what follows: “When Christ, who is our life, shall appear, then shall you also appear with Him in glory.” And what then shall we do now? “Be not envious because of the evil-doers, neither be envious against the workers of iniquity. For they shall soon wither like the grass, and fade like the herb of the meadow.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)