الآية رقم (24) - فَإِن لَّمْ تَفْعَلُواْ وَلَن تَفْعَلُواْ فَاتَّقُواْ النَّارَ الَّتِي وَقُودُهَا النَّاسُ وَالْحِجَارَةُ أُعِدَّتْ لِلْكَافِرِينَ

(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.”

The stones mentioned here are the idols that they used to worship.

Every time the Holy  Qur’an speaks about the hellfire, it will be followed by that on paradise.  Thus, the warnings are followed by the glad tidings.