6 “Shall not all know that work iniquity, that devour My people for the food of bread”?....There is therefore here a people of God that is being devoured. Nay, “There is not one that does good, there is not so much as one.” We reply by the rule above. But this people that is devoured, this people that suffers evil men, this that groans and travails amid evil men, now out of sons of men have been made sons of God: therefore are they devoured. For, “The counsel of the needy man you have confounded, because the Lord is his hope.” For ofttimes, in order that the people of God may be devoured, this very thing in it is despised, that it is the people of God.
I will pillage, he says, and despoil; if he is a Christian, what will he do to me?...But what follows? “I will convince you, and will set you before your face.” You will not now know so as you should be displeasing to yourself, you shall know so as you may mourn. For God cannot but show to the unrighteous their iniquity. If He is not to show, who will they be that are to say, “What has profited us pride, and what has boasting of riches bestowed upon us?” For then shall they know, that now will not know.
“Shall not all know?” etc. Why has He added, “for the food of bread”? As it were as bread, they eat My people. For all other things which we eat, we can eat now these, now those; not always this vegetable, not always this flesh, not always these apples: but always bread. What is then, “Devour My people for the food of bread”? Without intermission, without cessation they devour.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)