Tafsir of Al-Anbiya' 21:40

بل تٲتيهم بغتة

Nay, it will come upon them all of a sudden, means, the Fire will come upon them suddenly, i.e., it will take them by surprise.

فتبهتهم

and will perplex them, means, it will scare them, and they will succumb to it in confusion, not knowing what they are doing.

فﻼ يستطيعون ردها

and they will have no power to avert it, means, they will have no means of doing so.

وﻻ هم ينظرون

nor will they get respite. means, it will not be delayed for them even for an instant