is in the accusative case (mansub) by way of explanation (tafsir), and al-qayyim and al-mustaqim mean the same thing.
منصوبٌ عَلَى التَّفْسِيرِ، وَالْقِيَمُ وَالْمُسْتَقِيمُ فِي مَعْنَاهُمَا واحدٌ.
