You are reading a tafsir for the group of verses 46:31 to 46:34

یغْفِرْ‌ لَكُم مِّن ذُنُوبِكُمْ (will forgive your sins for you,) The word 'min' used in the text gives the sense of 'some'. If it is taken in this sense here, it would mean that 'some sins' will be forgiven by embracing Islam. It will indicate that only sins relating to the rights of Allah would be forgiven but not the rights of people. But some exegetes have taken 'min' in this verse as an extra word that has no additional meaning in Arabic idioms. Given this interpretation, no explanation is required.