ﻻ يقاتلونكم جميعا إﻻ في قرى محصنة أو من وراء جدر
They fight not against you even together, except in fortified townships, or from behind walls.
meaning, they will not fight Muslims except from behind besieged fortified forts, because of their cowardice and fear of Muslims. They only fight when they have to defend themselves (even though they threaten Muslims of reprisals.
Allah the Exalted said,
بٲسهم بينهم شديد
Their enmity among themselves is very great.
meaning, the enmity they feel against each other is intense,
It is as said,
ويذيق بعضكم بٲس بعض
And make you to taste the violence of one another. (6:65)
Allah said in the Ayah,
تحسبهم جميعا وقلوبهم شتى
You would think they were united, but their hearts are divided.
meaning, even though one might see them combining forces and think that these forces are harmonious, yet in reality, they are divided severely.
Ibrahim An-Nakha`i said that this Ayah refers to the hypocrites and the People of the Scriptures,
ذلك بٲنهم قوم ﻻ يعقلون
That is because they are a people who understand not.
Allah said,
كمثل الذين من قبلهم قريبا ذاقوا وبال أمرهم ولهم عذاب أليم