had they wanted to join your army they would have prepared themselves but god did not wish to motivate them so he caused them to linger behind with those whose joining you in battle would be of no use.
ولو أرادوا الخروج لأعدوا له عدة ولكن كره الله انبعاثهم فثبطهم وقيل اقعدوا مع القاعدين