Tafseer Ibn Kathir of AZ ZUMAR [35]

لِيُكَفِّرَ اللَّهُ عَنْهُمْ أَسْوَأَ الَّذِي عَمِلُوا وَيَجْزِيَهُمْ أَجْرَهُم بِأَحْسَنِ الَّذِي كَانُوا يَعْمَلُونَ

That Allah may remove from them the worst of what they did and reward them their due for the best of what they used to do.