17 Also, “I will satisfy her poor with bread;” what means this, brethren? Let us be poor, and we shall then be satisfied. Many who trust in the world, and are proud, are Christians; they worship Christ, but are not satisfied; for they have been satisfied, and abound in their pride. Of such it is said, “Our soul is filled with the scornful reproof of the wealthy, and with the despitefulness of the proud:” these have abundance, and therefore eat, but are not satisfied.
And what is said of them in the Psalm? “All such as be fat upon the earth have eaten and worshipped.” They worship Christ, they venerate Christ, they pray unto Christ; but they are not satisfied with His wisdom and righteousness. Wherefore? Because they are not poor. For the poor, that is the humble in heart, the more they hunger, the more they eat; and the more empty they are of the world, the more hungry they are. He who is full refuses whatsoever you will give him, because he is full.
Give me one who hungers; give me one of whom it is said, “Blessed are they that hunger and thirst after righteousness, for they shall be filled:” and these will be the poor of whom he has just said, “And will satisfy her poor with bread.” For in the very Psalm where it is said, “All such as be fat upon the earth have eaten and worshipped;” this is said of the poor also, and exactly in the same manner as in this Psalm, “The poor shall eat, and be satisfied: they that seek after the Lord shall praise Him.” Where it is said, “All such as be fat upon earth have eaten and worshipped:” it is said, “the poor shall eat, and be satisfied.”
Why, when the rich are said to have worshipped, are they not said to be satisfied; yet when the poor are mentioned, they are said to be satisfied? And whence are they satisfied? What is the nature, brethren, of this satisfying? God Himself is their bread. The bread came down upon the earth, that He might become milk unto us; and said to His own, “I am the Living Bread which came down from heaven.” Hence these words in the Psalm, “The poor shall eat, and be satisfied.” From what source shall they be satisfied? Hear what follows: “And they that seek after the Lord shall praise Him.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)