Who We Can Say Kafir?
We know that the Christians assumed that there are three forms of God. Actually, they believe in three gods, yet God called them the followers of Jesus, despite telling them that their belief in the Trinity is Kufr and shirk. God called them the followers of Jesus because they claimed to be the followers of Jesus. See the verse.3: 55 وَجَاعِلُ الَّذِينَ اتَّبَعُوكَ فَوْقَ الَّذِينَ كَفَرُوا إِلَىٰ يَوْمِ الْقِيَامَةِ If one believes there are two gods, they would explain why they think so. If they say that they do not accept the statement of the Quran that there is one God, this is a confession of kufr. They are no longer Muslim. It makes no sense to reject the Quran and stay Muslim. This is a contradiction that actually does not occur. And if they misinterpret the Quran to prove there are two gods in one God, as Christians do, they will be corrected, but their claim to be Muslim will be acceptable. Some sects of Muslims actually do shirk. They believe divine attributes are present in others and treat them as gods. But still they are called Muslims.