يَـٰٓأَيُّهَا ٱلنَّبِىُّ حَرِّضِ ٱلْمُؤْمِنِينَ عَلَى ٱلْقِتَالِ ۚ إِن يَكُن مِّنكُمْ عِشْرُونَ صَـٰبِرُونَ يَغْلِبُوا۟ مِا۟ئَتَيْنِ ۚ وَإِن يَكُن مِّنكُم مِّا۟ئَةٌ يَغْلِبُوٓا۟ أَلْفًا مِّنَ ٱلَّذِينَ كَفَرُوا۟ بِأَنَّهُمْ قَوْمٌ لَّا يَفْقَهُونَ ٦٥
O Prophet, urge the believers to battle. If there are among you twenty [who are] steadfast, they will overcome two hundred. And if there are among you one hundred [who are steadfast], they will overcome a thousand of those who have disbelieved because they are a people who do not understand.
Encouraging Believers to fight in Jihad; the Good News that a Few Muslims can overcome a Superior Enemy Force
Allah encourages His Prophet and the believers to fight and struggle against the enemy, and wage war against their forces. Allah affirms that He will suffice, aid, support, and help the believers against their enemies, even if their enemies are numerous and have sufficient supplies, while the believers are few. Allah said,
يَـأَيُّهَا النَّبِىُّ حَرِّضِ الْمُؤْمِنِينَ عَلَى الْقِتَالِ
(O Prophet! Urge the believers to fight), encouraged and called them to fight. The Messenger of Allah ﷺ used to encourage the Companions to fight when they faced the enemy. On the day of Badr when the idolators came with their forces and supplies, he said to his Companions,
Continue reading the tafsir of ayahs 64–66Ma'arif al-Qur'an
Mufti Muhammad Shafi
Mentioned for Muslims in the fourth (65) and fifth (66) verse, there is a law of war which stipulates the limit to which it was obligatory (fard) for them to stand resolutely against their adversary - and any retreat from which was a sin. In previous verses and events, it has been mentioned in detail that the unseen help of Allah Ta` ala is with Muslims for their matter is different, not like that of the peoples of the world at large. They, even if small in numbers, can overcome a lot more of their challengers as stated in the Holy Qur'an:
كَم مِّن فِئَةٍ قَلِيلَةٍ غَلَبَتْ فِئَةً كَثِيرَةً بِإِذْنِ اللَّـهِ
There are many smaller groups which overcome larger groups
with the will of Allah - 2:249).
Therefore, ten Muslims were declared to be equal to one hundred men in the first Jihad of Islam at the famous battle of Badr where the command given was:
إِن يَكُن مِّنكُمْ عِشْرُونَ صَابِرُونَ يَغْلِبُوا مِائَتَيْنِ ۚ وَإِن يَكُن مِّنكُم مِّائَةٌ يَغْلِبُوا أَلْفًا مِّنَ الَّذِينَ كَفَرُوا بِأَنَّهُمْ قَوْمٌ لَّا يَفْقَهُونَ
If there are twenty among you, who are patient, they will over-come two hundred; and if there are one hundred among you, they will overcome one thousand of those who disbelieve - 8:65
The style of expression used here is that of a welcome news flash - that one hundred Muslims shall overcome one thousand disbelievers. But, the purpose is to order that it is not permissible for one hundred Muslims to run against one thousand disbelievers. The wisdom behind using the style of news is to make the hearts of Muslims become strong with this glad tidings telling them that Allah is promising their safety and victory. Had this order been announced in the imperative mood as a law, it would have naturally weighed heavy on temperaments.
The encounter at Badr was the very first battle Muslims had ever fought. At that time, they were in a terrible condition. The total number of Muslims itself was insignificant. Then, all of them had not gone to the war front. The hard fact was that only those who could get ready on the spot were the ones who became the 'army' of this war. Therefore, in this Jihad, one hundred Muslims were commanded to confront one thousand disbelievers in a style which carried the promise of Divine help and support.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.