If a man insists that something is true, in spite of the fact that it is not so proved by the book of God, it means that he is holding others equal to God. In other words, he is giving to those other than God the right to devise his religion for him. This is a very serious matter. The fact is that the right to decide upon or formulate anything in the nature of religion (din) rests with the one and only God. To entrust this right to anybody other than God is obviously engaging in polytheism (ascribing partners to God), and this is absolutely unpardonable in the eyes of God.