(وَيَحْلِفُونَ بِاللَّهِ إِنَّهُمْ لَمِنكُمْ…) (And they swear by Allah that they are from among you,): When people are faced with rejection, they swear to establish the validity of the matter. The hypocrite always swears without being asked, as an oath happens when there are doubts and rejection, they swear because they believe that people secretly entertain doubts about them, because they are hypocrites.

…وَلَٰكِنَّهُمْ قَوْمٌ يَفْرَقُونَ  (but they are a people who are always afraid.): They are afraid because they believe that at any moment, their affairs might be exposed, and their secrets and conspiracies might be revealed.