﴿ إِنَّمَا يَسْتَـْٔذِنُكَ ٱلَّذِينَ لَا يُؤْمِنُونَ بِٱللَّهِ وَٱلْيَوْمِ ٱلْءَاخِرِ وَٱرْتَابَتْ قُلُوبُهُمْ فَهُمْ فِى رَيْبِهِمْ يَتَرَدَّدُونَ ﴾

“only those ask thee for exemption who do not [truly] believe in God and the Last Day and whose hearts have become a prey to doubt, so that in their doubting they waver between one thing and another.”

They alone ask leave of you to stay behind who do not believe in God and the Last Day and whose hearts are doubtful uncertain about religion so in their doubt they waver they are confused.