وَتَحْمِي عَنِ النُّكْرِ وَلَا تَتَحَامَاهُ
You restrain others from wrongdoing but do not keep away from it yourself.
Al-nukr is a blameworthy deed. Taḥmī here concerns preventing another person, while tataḥāmāhu means protecting oneself by staying clear of it.
The contrast is exact: prohibiting wrong for others without avoiding it oneself.