28 Grain must be ground to make bread; so one does not go on threshing it forever. The wheels of a threshing cart may be rolled over it, but one does not use horses to grind grain.

Read Isaiah 28:28 Using Other Translations

Bread corn is bruised; because he will not ever be threshing it, nor break it with the wheel of his cart, nor bruise it with his horsemen.
Does one crush grain for bread? No, he does not thresh it forever; when he drives his cart wheel over it with his horses, he does not crush it.
Grain for bread is easily crushed, so he doesn’t keep on pounding it. He threshes it under the wheels of a cart, but he doesn’t pulverize it.