The Assyrian messenger launches a campaign of psychological warfare against the besieged people of Jerusalem, offering them a tempting alternative to their current leadership. By urging the people to ignore King Hezekiah, the messenger is actively inciting a rebellion. He promises that a much safer and better life awaits them under the protection of the Assyrian empire [מלבי״ם, ביאור שטיינזלץ].
To secure this new reality, the Assyrian king demands a gesture of peace. The primary approach among commentators is that this requires formalizing a treaty of reconciliation, complete with a tribute that signals their complete surrender [רש״י, מצודת דוד, מצודת ציון, ביאור שטיינזלץ]. On the other hand, some maintain that the demand is an expectation of affection rather than just politics. Because the trapped citizens have no real chance of escape, they are expected to surrender not just in action, but with a public display of love and goodwill toward their conquerors [שד״ל].
The people are commanded to leave the safety of their city walls and walk out to the enemy camp. This act is intended to be a formal welcoming ceremony for the Assyrian king, serving as undeniable public proof that they have accepted his absolute authority [מלבי״ם, רש״י, ביאור שטיינזלץ].
In exchange for this surrender, the Assyrians offer a promise that speaks directly to the physical desperation of the trapped citizens. They are told that the siege will be lifted instantly, saving them from starvation. Each person will finally be able to leave the city in total safety to harvest their own fruit and draw water from their own wells [מלבי״ם, מצודת דוד]. Yet, this promised peace is only an illusion of permanence. The Assyrian strategy is to allow the residents a brief period of calm in their own homes just until a suitable replacement land can be found. Ultimately, they will be sent away, falling victim to the standard Assyrian policy of uprooting conquered nations and relocating them far from their homelands [רש״י].