Adam Clarke on Ezekiel 4:3

Take thou unto thee an iron pan - מחבת machabath, a flat plate or slice, as the margin properly renders it: such as are used in some countries to bake bread on, called a griddle or girdle, being suspended above the fire, and kept in a proper degree of heat for the purpose. A plate like this, stuck perpendicularly in the earth, would show the nature of a wall much better than any pan could do. The Chaldeans threw such a wall round Jerusalem, to prevent the besieged from receiving any succours, and from escaping from the city.

This shall be a sign to the house of Israel - This shall be an emblematical representation of what shall actually take place.