What does it mean to "grind the faces of the poor"?

I remember a Sunday School teacher talking about this scripture. For some reason I pictured someone putting another's face to a millstone. The kind that is used to grind grain into flour. I imagined that they were doing it do they could glut themselves from the labor of the other.

Avarice is a trap that we must all guard ourselves against. We must " not suffer that the beggar putteth up his petition to you in vain, and turn him out to perish....For behold, are we not all beggars? Do we not all depend upon the same Being, even God, for all the substance which we have"? (Mosiah 4:16-19)

On the other hand, to those that are poor, King Benjamin says, "I would that ye say in your hearts that: I give not because I have not, but if I had I would give. And now, if ye say this in your hearts ye remain guiltless, otherwise ye are condemned; and your condemnation is just for ye covet that which ye have not received." (Mosiah 4:24-25)

From a FB Post