Muhammad said: The interpretation of "how" is an interrogation in the sense of amazement. It is directed at the believers; meaning: Wonder at these people; how can they disbelieve when the proof of Allah has been established against them?!
قَالَ مُحَمَّد: تَأْوِيل ((كَيفَ)) اسْتِفْهَام فِي معنى التَّعَجُّب؛ إِنَّمَا هُوَ للْمُؤْمِنين؛ أَي: اعجبوا من هَؤُلاءِ؛ كَيفَ يكفرون وَقد ثبتَتْ حجَّة الله عَلَيْهِم؟!