ثُمَّ تَوَلَّيْتُم مِّن بَعْدِ ذَلِكَ فَلَوْلَا فَضْلُ اللَّهِThen after that you turned away. Had it not been for the grace of Allah,means, "Yet, after the firm pledge that you gave, you still deviated and broke your pledge";فَلَوْلَا فَضْلُ اللَّهِ عَلَيْكُمْ وَرَحْمَتُهُHad it not been for the grace and mercy of Allah upon you,meaning, by forgiving you and by sending the Prophets and Messengers to you.لَكُنتُم مِّنَ الْخَاسِرِينَIndeed you would have been among the losers.meaning, in this life and the Hereafter due to their breach of the covenant