"And Allah had already given you victory at Badr while you were few in number," He is reminding them of His favor upon them. Qatadah said: Allah gave them victory on the day of Badr with a thousand angels reinforcing them.
﴿وَلَقَدْ نَصَرَكُمُ اللَّهُ بِبَدْرٍ وَأَنْتُمْ أَذِلَّة﴾ يذكرهم نعْمَته عَلَيْهِم. قَالَ قَتَادَة: نَصرهم الله يَوْم بدر بِأَلف من الْمَلَائِكَة مُردفِينَ