فَأَنْذَرْتُكُمْ نَارًا تَلَظَّىٰ لَا يَصْلَاهَا إِلَّا الْأَشْقَى الَّذِي كَذَّبَ وَتَوَلَّىٰ
Therefore I have warned you of a blazing fire; the most wretched, who denied and turned away, is singled out in this threat. (92:14–16)
Fa-andhartukum turns the preceding assurance into a consequential warning. The indefinite nāran, qualified by talaẓẓā, intensifies the image. Lā ... illā is a restrictive frame; the relative clause identifies the condemned disposition.
The scope of the restriction must be read in the threat context. A rhetorical lesson should not construct a sweeping doctrinal proposition from an isolated sentence without considering the rest of the relevant discourse.