What happens when the ground beneath your feet becomes as unyielding as iron? This imagery speaks of utter barrenness and futility.
The earth underfoot turning to iron signifies a complete inability to cultivate and produce. Iron is hard, dense, and impenetrable. The soil, once fertile and responsive to the rain, becomes like a metallic slab. The plow cannot break it, seeds cannot penetrate it, and nothing can grow. This represents the utter failure of all labor and effort. Every attempt to farm, to build, to sow will be met with unyielding resistance, producing nothing of value. It's the opposite of the promised land flowing with milk and honey; it's a land that offers only dust and despair, reflecting that even the most basic sustenance is withheld.