But if you do not - and you will never be able (2:24)

﴿فَإِن لَّمْ تَفْعَلُوا وَلَن تَفْعَلُوا فَاتَّقُوا النَّارَ الَّتِي وَقُودُهَا النَّاسُ وَالْحِجَارَةُ ۖ أُعِدَّتْ لِلْكَافِرِينَ﴾
[ البقرة: 24]

2:24 But if you do not - and you will never be able to - then fear the Fire, whose fuel is men and stones, prepared for the disbelievers.

If they are unable to do so – and they will never be able to do it – they should be mindful of the fire of Hell, which burns with people who deserve the torment, and with the idols which they used to worship instead of Allah: punishing both the idol-worshipers and what they worshiped.
The fire of Hell has been prepared as a punishment for the disbelievers.

But if you do it not, and you can never do it, then fear the Fire (Hell) whose fuel is men and stones, prepared for the disbelievers.

phonetic Transliteration

Fain lam tafAAaloo walan tafAAaloo faittaqoo alnnara allatee waqooduha alnnasu waalhijaratu oAAiddat lilkafireena

Abdullah Yusuf Ali - Translation

But if ye cannot- and of a surety ye cannot- then fear the Fire whose fuel is men and stones,- which is prepared for those who reject Faith.

Safi-ur-Rahman al-Mubarakpuri

But if you do it not, and you can never do it, then fear the Fire (Hell) whose fuel is men and stones, prepared for the disbelievers.

Page 4 English transliteration