The powerful imagery of a city acting as a sturdy pot and its residents as the meat within it originally conveyed a deep sense of security. Yet, this comforting metaphor is suddenly turned upside down for the people of Jerusalem, exposing a much darker and bitter reality. The illusion of safety is completely shattered. Jerusalem will not act as a protective barrier, nor will it keep the people safe the way a pot contains and guards meat until the cooking is finished [רש״י, מצודת דוד, רד״ק, ביאור שטיינזלץ]. Instead, the walls of the city will be breached [מלבי״ם], and the inhabitants will be denied the privilege of living out their days in peace within their home [מצודת דוד, רד״ק].
Even though the city will fail to protect them, the residents will still resemble meat inside a pot in a terrifying way. They will endure intense and agonizing suffering while trapped inside. Rather than finding shelter, they will undergo a brutal cooking process, breaking down, melting, and wasting away from their misery, much like pieces of meat falling apart in a boiling cauldron [רש״י, מצודת דוד, רד״ק, ביאור שטיינזלץ].
Despite the severe torment experienced inside Jerusalem, their final doom will actually unfold outside the city walls. The primary approach among commentators is that the people will not meet their end within Jerusalem itself. Instead, their death sentences and the climax of their suffering will be carried out far away on the very borders of the land, specifically in the region of Riblah [רש״י, מצודת דוד, רד״ק]. Offering a different perspective, another viewpoint emphasizes that facing judgment on the border actually serves to prevent them from reaching exile in Babylon. By dying on the edge of the land, their fate is sealed in such a way that it is fundamentally as if they never managed to escape the boiling pot at all [מלבי״ם].