The first commandment says: God is One; God is the King and the Ruler, and they conjugate others with Him: God is Zealous: does not agree about anyone be a peer along with Him.
Such peers may be like Jesus Christ, the saints, Ezra and the Jewish rabbis, Ali and his descendents, etc.
So it is this conjugation of peers with God is the grievous sin, which is against the religion of God.
In other words: some people conjugate (Jesus, Mohammed, Ali, Moses and others) with God in the worship while God refuses any sort of conjugating others with Him.
Such peers may be like Jesus Christ, the saints, Ezra and the Jewish rabbis, Ali and his descendents, etc.
So it is this conjugation of peers with God is the grievous sin, which is against the religion of God.
In other words: some people conjugate (Jesus, Mohammed, Ali, Moses and others) with God in the worship while God refuses any sort of conjugating others with Him.