19 Sometimes, however, and we must not pass over this without mention, you find a poor man proud, and a rich man humble: we daily endure such persons. You hear a poor man groaning beneath a rich man, and when the more powerful rich man presses upon him, then you see him humble: sometimes not even then, but even then proud; whence you see what he would have been, had he any property. God's poor one is therefore poor in spirit, not in his purse. Sometimes a man goes forth having a full house, rich lands, many estates, much gold and silver; he knows that he must not trust in these, he humbles himself before God, he does good with them; thus his heart is raised unto God, so that he is aware that not only do riches themselves profit him nothing, but that they even impede his feet, save He rule them, and aid them: and he is counted among the poor who are satisfied with bread.
Thou findest another a proud beggar, or not proud only because he has nothing, nevertheless seeking whereby he may be puffed up. God does not heed the means a man has, but the wish he has, and judges him according to his wish for temporal blessings, not according to the means which it is not his lot to have. Whence the Apostle says of the rich, “Charge them that are rich in this world, that they be not highminded, nor trust in uncertain riches, but in the living God, who gives us richly all things to enjoy.”
What therefore should they do with their riches? He goes on to say: “That they be rich in good works, ready to distribute, willing to communicate.” And see that they are poor in this world: “Laying up in store for themselves,” he adds, “a good foundation against the time to come, that they may lay hold on eternal life.” When they have laid hold of eternal life, then will they be rich; but since they have it not as yet, they should know that they are poor. Thus it is that God counts among His poor all the humble in heart, who are established in that twofold charity, whatever they may have in this world— among His poor, whom He satisfies with bread.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)