"It is only those who do not believe in Allah and the Last Day who ask your permission," out of aversion to Jihad, "and their hearts have wavered," meaning: they have doubted concerning Allah, may He be exalted, and His religion.
﴿إِنَّمَا يستئذنك الَّذِينَ لَا يُؤْمِنُونَ بِاللَّهِ وَالْيَوْمِ الآخر﴾ كَرَاهِيَة للْجِهَاد ﴿وارتابت قُلُوبهم﴾ أَيْ: شَكَّتْ فِي اللَّهِ ﷿ وَفِي دينه