﴿ إِذْ يُرِيكَهُمُ ٱللَّهُ فِى مَنَامِكَ قَلِيلًۭا ۖ وَلَوْ أَرَىٰكَهُمْ كَثِيرًۭا لَّفَشِلْتُمْ وَلَتَنَٰزَعْتُمْ فِى ٱلْأَمْرِ وَلَٰكِنَّ ٱللَّهَ سَلَّمَ ۗ إِنَّهُۥ عَلِيمٌۢ بِذَاتِ ٱلصُّدُورِ ﴾

“Lo! God showed them to thee in a dream as few: for, had He shown them to you as many, you would surely have lost heart, and would surely have disagreed with one another about what to do. But God saved [you from this]: verily, He has full knowledge of what is the hearts [of men].”

At Badr the Quraysh had a large army. Had the Muslims seen their real numbers, some of them would have said that they should fight, while others would have asked not to fight. In this way differences would have cropped up and the real task would have remained unfinished. So, God showed their numbers to Muslims as fewer while he showed the number of Muslims to the Quraysh as more. In this way it was possible for the Muslims to fight fearlessly. When God wants a task to be performed, He sends help and arranges for its completion. The events that occur during the course of action occur at God’s behest, so that He may judge the reaction of the person concerned to the conditions set by Him.