وَخَيْرُ الْخَطَّائِينَ التَّوَّابُونَ makes the response to wrongdoing the decisive moral point: does the person turn back and reform, or defend the error? Constant excuses, blaming others, and dismissing infringed rights obstruct change.
خَيْرُ means “better/best,” while الْخَطَّائِينَ completes the construct as its genitive complement, producing “the best of those who err.”
Apologizing, honoring a neglected promise, or repaying a debt demonstrates that repentance has consequences in conduct, not only in words.