أَخَذْنَ عَلَى بُعُولَتِهِنَّ عَهْدًا
They exacted a pledge from their husbands.
إِذَا لَاقَوْا كَتَائِبَ مُعْلِمِينَا
Whenever they encounter marked battle units.
لَيَسْتَلِبُنَّ ...
They must seize spoils from their opponents.
The condition begins in one verse and is resolved in the next. The emphatic lām and nūn heighten the demand. Reading the verses together reveals the complete syntactic force.