﴿ وَذَٰلِكُمْ ظَنُّكُمُ ٱلَّذِى ظَنَنتُم بِرَبِّكُمْ أَرْدَىٰكُمْ فَأَصْبَحْتُم مِّنَ ٱلْخَٰسِرِينَ ﴾

“and that very thought which you thought about your Sustainer has brought you to perdition, and so now you find yourselves among the lost!””

And that wa-dhālikum the subject supposition of yours zannukum substitutes for it which you supposed of your Lord alladhī zanantum bi-rabbikum a descriptive clause; the predicate is the following ardākum has ruined you that is it has brought about your destruction. So you have become among the losers’.