﴿ إِن يَنصُرْكُمُ ٱللَّهُ فَلَا غَالِبَ لَكُمْ ۖ وَإِن يَخْذُلْكُمْ فَمَن ذَا ٱلَّذِى يَنصُرُكُم مِّنۢ بَعْدِهِۦ ۗ وَعَلَى ٱللَّهِ فَلْيَتَوَكَّلِ ٱلْمُؤْمِنُونَ ﴾

“If God succours you, none can ever overcome you; but if He should forsake you, who could succour you thereafter? In God, then, let the believers place their trust!”

If God helps you if He gives you assistance against your enemy as on the Day of Badr then none can overcome you; but if He forsakes you if He refrains from assisting you as on the Day of Uhud then who is there who can help you after Him? that is after His forsaking you? In other words there is no one to help you. Therefore on God and on no one else let the believers rely.