John Gill Commentary Isaiah 3:15

"what mean ye that ye crush my people, and grind the face of the poor? saith the Lord, Jehovah of hosts." — Isaiah 3:15 (ASV)

What mean you, [that] you beat my people to pieces
Reduce them to the utmost poverty; so the Targum, "wherefore do you impoverish my people?" as they did by exacting tithes of all that they possessed; by requiring large sums for their long prayers; and by various traditions they enjoined them to observe.

and grind the faces of the poor ?
either by smiting them on the cheek, as Christ, who became poor for our sakes, was smitten by them; or by bringing them into such low circumstances, by their exorbitant demands, that they had not sufficiency of food to eat; by which means their faces became pale, thin, and meagre.

saith the Lord God of Hosts :
who saw all their actions, and was able to plead his people's cause, and take vengeance on their oppressors.