فَهَزَمُوهُم بِإِذْنِ ٱللَّهِ وَقَتَلَ دَاوُۥدُ جَالُوتَ وَءَاتَىٰهُ ٱللَّهُ ٱلْمُلْكَ وَٱلْحِكْمَةَ وَعَلَّمَهُۥ مِمَّا يَشَآءُ ۗ وَلَوْلَا دَفْعُ ٱللَّهِ ٱلنَّاسَ بَعْضَهُم بِبَعْضٍ لَّفَسَدَتِ ٱلْأَرْضُ وَلَـٰكِنَّ ٱللَّهَ ذُو فَضْلٍ عَلَى ٱلْعَـٰلَمِينَ
Thus they defeated them by Allah’s grace, and David killed Goliath, and Allah gave him the kingdom and wisdom and taught him whatever He willed[139]. Were it not for Allah to repel some people by others, the earth would be filled with corruption, but Allah is All-Gracious to the worlds.
They defeated them by God’s will. The prophet of God, David, killed their leader Goliath and God gave him kingship and prophethood and taught him many sciences as He willed, including those that are beneficial for this world and those for the hearafter. If it were not the system of God to drive back the evil of some people by means of others, there would be corruption on earth as the evil ones would gain authority. However, God is Bountiful to all of His creation.