Divine justice often operates with a tragic, measure-for-measure irony. When the people stubbornly refused to grant freedom to their slaves, they triggered a devastating response. By denying their servants liberty [מצודת דוד], they simultaneously violated two distinct agreements: the ancient covenant of the Torah requiring the liberation of servants, and a new agreement they had just made among themselves [מלבי״ם].
In response to their actions, God grants a terrifying and destructive kind of freedom. The primary approach among commentators is that this liberty is actually a total withdrawal of Divine protection. Being a servant of God comes with the profound benefit of being shielded from the random cruelties of fate. Therefore, when God releases the people from His service, He is effectively announcing that He is no longer their master. They are abandoned and left completely exposed to the ravages of the sword, disease, and starvation, with no higher power left to defend them [רש״י, רד״ק, מצודת דוד, מלבי״ם].
Another perspective understands this divine declaration of freedom differently. Rather than abandoning the people, God is releasing the forces of destruction. Because the nation refused to emancipate its slaves, God emancipates His own servants, namely the plagues and disasters. He grants these destructive forces total freedom to sweep through the besieged residents of Jerusalem and leave ruin in their wake [ביאור שטיינזלץ].
The consequence of this horrific freedom is absolute devastation. The people will be reduced to a state of constant trembling and endless wandering, becoming an object of terror to all the kingdoms of the earth [מצודת ציון, רד״ק]. The surrounding nations will fill them with dread [מצודת דוד], and Jerusalem itself will be transformed into a nightmare. Unlike other cities that survived conquest, Jerusalem will be reduced to a complete heap of ruins [ביאור שטיינזלץ].