فَتُصِيبَكُم مِّنْهُم مَّعَرَّةٌ بِغَيْرِ عِلْمٍ (and thus an embarrassing situation might have befallen you because of them unknowingly....48:25): According to some authorities on lexicology ma'arrah connotes "sin"; according to others it means "harm"; and other authorities say it denotes "shame" or "embarrassment". In this context, apparently the last meaning appears to be apt. There was a nucleus of Muslims in Makkah and if the fight had broken out, Muslim army would have unwittingly killed their own Muslim brethren in faith, thereby causing great injury to their own cause, and incurring obloquy and opprobrium for themselves.
Natural Safeguard of the Noble Companions against Mistakes
Imam Qurtubi says that if a Muslim unknowingly kills another Muslim, it is not a sin or crime. It is, however, certainly a source of shame, embarrassment and regret. Since it is a Qatl Khata', the laws of diyah [ blood-wit ] will apply. Allah has protected the noble Companions ؓ against this as well. This shows the noble Companions ؓ are not infallible like the prophets of Allah, but Allah has in general terms safeguarded them in a natural way against mistakes which would be a cause of embarrassment, obloquy and opprobrium to them.
لِّيُدْخِلَ اللَّـهُ فِي رَحْمَتِهِ مَن يَشَاءُ (so that Allah may admit to His mercy whom He wills...48:25): It means that Allah infused patience in Muslims on this occasion to avoid war, because He knew that many people in future would embrace Islam on whom His mercy will be showered. Similarly the nucleus of Muslims who were detained in Makkah will also receive a large share of His mercy.
لَوْ تَزَيَّلُوا (And if they [ the believing men and women ] had been separate, [ from disbelievers ], We would surely have punished those of them who disbelieved....48:25) Lexically, the word tazayyul denotes 'separation'. The sense is that if Muslims detained in Makkah had been separate and distinct from the unbelievers, the Muslims coming from Madinah would have been able to save them in case of war, and Allah would have had the disbelievers punished then and there, because that was the demand of their attitude. However, the Makkan society at that time was a mixed society - helpless Muslim men and women and non-Muslims were living together. The Muslims were indistinguishable from non-Muslims. If fighting had broken out, there would have been no way to save the Muslims. Therefore, Allah averted the war.