الَّذِي يَصْلَى النَّارَ الْكُبْرَىٰ ۞ ثُمَّ لَا يَمُوتُ فِيهَا وَلَا يَحْيَىٰ
Who enters the greatest Fire, then neither dies there nor truly lives. (87:12–13)
The relative clause characterizes “the most wretched.” Thumma moves the discourse to a later condition, while the paired negations deny both the finality of death and the relief normally associated with life.
This is not best read as a flat logical contradiction. “Lives” here is understood in the sense of a life possessing comfort or benefit. The paired negatives intensify the picture of punishment.