The dialogue between Lot and the heavenly messenger captures a rare moment where a divine decree is altered in response to a human plea. When God dispatches angels on a mission, He grants these intelligent beings a degree of authority to adjust their task based on their own judgment [רד״ק, ברכת אשר על התורה]. Hearing Lot's desperate request, the angel confirms that his petition is accepted [הכתב והקבלה, ביאור שטיינזלץ]. The primary approach among commentators is that the angel grants a double favor. Not only does he agree to spare Lot's life, but he also agrees to save an entire city from ruin for his sake [רש״י, מזרחי, בכור שור, חזקוני, ביאור שטיינזלץ]. Interestingly, Lot only asked for a safe place to hide, yet the angel goes above and beyond, choosing to spare the location completely [העמק דבר].
The city of Zoar was originally destined to be destroyed alongside the other major cities of the region, including Sodom, Gomorrah, Admah, and Zeboiim. Its survival is entirely dependent on Lot seeking refuge there [ביאור שטיינזלץ, ברכת אשר על התורה]. The impending destruction advanced geographically from one place to the next. Consequently, the angel urges Lot to hurry, explaining that the disaster cannot be held back from striking Zoar until Lot is safely inside its borders [מלבי״ם].
A fascinating question remains about whether Zoar was spared permanently. The primary approach among commentators is that the city was completely saved. However, an alternative view questions how Lot's merit could possibly be enough to save an entire population, considering that even Abraham could not achieve such a rescue through his prayers. According to this perspective, the angel never promised a permanent pardon. Instead, he merely delayed the disaster for a short time so Lot could rest from his exhausting journey. Ultimately, the wave of destruction swept over Zoar as well. This temporary reprieve explains why Lot later became terrified to stay in the city and quickly fled into the mountains [ביאור יש״ר].