Now the positioning of “then fear the Fire whose fuel is men and stones (fa-’ttaqū al-nār allatī waqūduhā an-nās wa al-ḥijāra):” consider this: “and if you cannot” being followed by “then fear” necessitates according to the tastes of eloquence the following implied sentences: “Since you haven’t been able to do it and you won’t be able to, it’s obvious it’s miraculous, so it [must be] Allah’s word. Hence it is incumbent on you to believe in it and comply with its commands. And one of its commands is ‘O you people! Worship!,’ that you may fear Hell-fire, so fear the Fire!” See how concise it is, how miraculous!
The positioning of “whose fuel is men and stones (allatī waqūduhā al-nās wa al-ḥijāra):” the purpose of “then fear (fa-’ttaqū)” is to frighten, and [here, being followed by “the Fire”] it has a strengthened, intensified meaning, in order to terrify them with “whose fuel is men.” For a fire fuelled by human beings is more appalling and horrifying. Then it further intensifies it by adding stones. For [the fire] that burns stones is even fiercer. It also infers that it is restraining them from idolatry. That is, if you don’t comply with Allah’s command and you worship stone idols, you will enter the Fire that consumes both worshippers and their objects of worship.
The positioning of “prepared for those who reject faith (u‘iddat li’l-kāfirīn):” this elucidates and establishes the consequence (luzūm) between the conditional verb “if you cannot” [the protasis] and its apodosis “then fear.” That is, this calamity is not like storm and tempest and other [natural] disasters which do not strike wrongdoers alone but encompass the righteous and elect; it is particular to offenders and caused by disbelief, and the only means of salvation from it is to comply with the Qur’an.
Moreover, “prepared (u‘iddat)” indicates that Hell is created and existent at the present moment, contrarily to what the Mu‘tazilites asserted. The following will show you, and allow you to surmise, that Hell is eternal: if you reflect on the world from the point of view of wisdom (al-ḥikma), you will see fire to be a vast creature, prevailing and overwhelming, a primordial element of the lofty and lower worlds. And you will understand that it consists of a huge head and strange fruits that hang over into eternity. Don’t you see that someone who espies a long stalk trailing along [the ground] will understand there to be a melon at the end of it; similarly whoever sees the creatures of fire will understand that at their extremity are the bitter fruits of Hell. Likewise, whoever sees bounties and good things and pleasures will surmise that their extracts and the place they are poured out and their garden is Paradise.