يَٰٓأَيُّهَا ٱلنَّبِىُّ حَرِّضِ ٱلْمُؤْمِنِينَ عَلَى ٱلْقِتَالِ ۚ إِن يَكُن مِّنكُمْ عِشْرُونَ صَٰبِرُونَ يَغْلِبُوا۟ مِا۟ئَتَيْنِ ۚ وَإِن يَكُن مِّنكُم مِّا۟ئَةٌ يَغْلِبُوٓا۟ أَلْفًا مِّنَ ٱلَّذِينَ كَفَرُوا۟ بِأَنَّهُمْ قَوْمٌ لَّا يَفْقَهُونَ
4:85.
Commentary:
As disbelievers were not going to desist from fighting, as they were invited to do (8:23 & 8:39 above), but were determined to carry on war of aggression against Islam, therefore the Holy Prophet has been asked in this verse to urge Muslims also to fight in self-defence.
The verse promises victory to Muslims over an enemy ten times their number because they are a people who do not understand. Fighters should understand the purpose of their fighting. They should look upon the war, they are engaged in, as their own. They should know the advantage which will accrue to their community if they win, and they should also know the losses which they will have to suffer if they are defeated. Mere hirelings, or men, who are blindly led to war by their leaders but who do not understand its object and feel no personal interest in it, cannot win. The forces that fought against Islam were mostly composed of men, who took part in the war merely because they were called upon to do so by their mischievous leaders-the wicked and avowed enemies of Islam. They felt no personal interest in the war against the new religion.
Religiously speaking also, they were a people who did not "understand", whereas Muslims did understand what faith meant. They were moved by love for their God, their Prophet and their religion. Disbelievers, on the other hand, were not as devoted to their idols as the Faithful were to their God in Whom they had a living faith.
The verse gives the number twenty as the minimum number for Muslims to win sure victory over their enemy because that was the least number that made a regular fighting party. If the number of men was less than twenty, it was not to be regarded as a fighting force and the laws relating to war did not apply to them.
Thus, a party of twenty persons, the minimum comprising a fighting unit, was bound to fight if they met an enemy as many as ten times their strength, and they were forbidden to flee. The question of retiring before the enemy is not to be decided by the men but by their officers, who may act as they may think best in the interest of war. See also 8:16.
4:85.
The verse seems to give 20 as the minimum number that makes a fighting party.
Because they are mercenaries, and do not realize the righteousness of the cause they fight for, they feel no real interest for it. Or the meaning may be that they have no higher ideals which they seek to pursue and serve.