كَلَّNay,This is a participle that opposes what came before it and gives emphasis to what follows it.سَنَكْتُبُ مَا يَقُولُWe shall record what he says,what he is seeking, and his idea that he has given himself about what he hopes for, and his disbelief in Allah the Most Great.وَنَمُدُّ لَهُ مِنَ الْعَذَابِ مَدًّاWe shall increase his torment.This is referring to what will happen in the abode of the Hereafter, because of his saying his disbelief in Allah in this life