The three West-Asian, Abrahamic religions óJudaism, Christianity, and Islamó are radically monotheistic. One of the central doctrines in these faiths is the categorical rejection of any divine being or beings other than God, the One Supreme Being. These three monotheistic religions differ from each other in their interpretations of monotheism. They are also immensely diverse within themselves, each incorporating a broad spectrum of divergent beliefs.
Judaism, the oldest, began to set itself apart from religions with many gods by as early as 2000 B.C.E, in practicing monolatry, the worship of one God. By the sixth century B.C.E. Judaism had developed belief in monotheism, that there is only one God. It holds that anyone can know and worship the one God, but that the Jewish people have been called by God to a particular obedience and worship.
Christianity has traditionally given an exclusivist interpretation of monotheism: that only Christians can know and worship the one God. Conservative branches of Christianity still hold that the one God has only revealed himself to Christians and all other religions worship false gods who do not exist. Other branches of Christianity hold views more in line with those of Judaism. However, even conservative Christians put Judaism in a special category as worshipping the one true God worshipped by Christians.
Islam was founded on the premise that there is one God who is worshipped by all monotheistic religions. But it teaches that Islam is the latest, and therefore the most pure revelation of that one God.
Zoroastrianism, another ancient West-Asian religion, is also monotheistic. Following the teachings of the prophet Zoroaster and the Avesta scriptures, Zoroastrians believe that the prophet was renewing the original eternal truth that has always been known. They believe that the righteous of all religions follow the same eternal truth and will attain the rewards of heaven. The same one God has placed each person in a particular religion which that person should follow.
Likewise the Sikh religion, originating in the fifteenth century in North India, is monotheistic, emphasizing the essential Oneness of God. God is not many in the many religions, but One. Sikhism was founded by Guru Nanak Dev on the basis of the belief that the eternal truths of Hinduism and of Islam were in fact the same eternal Truth, given by the same One God.
The monotheism of Sikhism, like that of Judaism and Islam, rejects both iconographic representations and anthropomorphic characterizations of God. God is not, and cannot be, or take on, human form. The monotheism of Christianity, on the other hand postulates a single Godhead which incorporates three distinct persons, one of whom has taken on human form in historical time, to bring salvation and renew God's truth in the world.
It must be noted, however, that any short characterization such as this can only give a general indication of the wide variety of beliefs which are included within these religions.