Jamieson, Fausset and Brown on Ezekiel 4:3

3. iron pan--the divine decree as to the Chaldean army investing the city.

set it for a wall of iron between thee and the city--Ezekiel, in the person of God, represents the wall of separation between him and the people as one of iron: and the Chaldean investing army. His instrument of separating them from him, as one impossible to burst through.

set ... face against it--inexorably (Psa 34:16). The exiles envied their brethren remaining in Jerusalem, but exile is better than the straitness of a siege.