11 Therefore that man having been condemned that “has trusted in the multitude of his riches, and has prevailed in his vanity:” for what more vain, than he that thinks coin more to avail than God? Therefore that man having been condemned that said, blessed of the people to whom these things are: thou that sayest, “Blessed the people of whom is the Lord their own God,” dost think of yourself what? dost hope for yourself what? “But I;” now at length hear that body: “But I am like an olive, fruit-bearing in the house of God”.
Not one man speaks, but that olive fruit-bearing, whence have been pruned the proud branches, and the humble wild olive graffed in. “Like an olive, fruit-bearing in the house of God, I have trusted in the mercy of God.” He did what? “In the multitude of his riches:” therefore his root shall be plucked out from the land of the living. “But I,” because “like an olive, fruit-bearing in the house of God,” the root whereof is nourished, is not rooted out, “have trusted in the mercy of God.”
But perchance now? For even herein men err sometimes. God indeed they worship, and are not now like to that Doeg: but though on God they rely, it is for temporal things nevertheless; so that they say to themselves, I worship my God, who will make me rich upon earth, who to me will give sons, who to me will give a wife. Such things indeed gives none but God, but God would not have Himself for the sake of such things to be loved. For to this end oftentimes those things He gives even to evil men, in order that some other thing good men of Him may learn to seek.
In what manner then do you say, “I have trusted in the mercy of God”? Perchance for obtaining temporal things? Nay but, “For everlasting and world without end.” The expression, “For everlasting,” he willed to repeat by adding, “world without end,” in order that by there repeating he might affirm how rooted he was in the love of the kingdom of heaven, and in the hope of everlasting felicity.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)