The term monotheism comes from the Greek words monos 'single', and theos 'god'. It is prevalent in many cultures across the globe. Although the differences between monotheism, polytheism, and atheism are clear, it should not be confused with henotheism, i.e., one supreme god above a group of lesser gods. Advocates of this philosophy say that this is the ideal that all religions should work to attain, and that believing in one supreme god who is ubiquitous and omniscient is the most logical way to perceive god.
That debate can be kept for another day. For now, let us have a look at a few examples of the monotheistic religions of the world.
Ancient Judaism was divided into many cults, with the God Yahweh reigning supreme over lesser Gods. However, around the end of the 7th century, the priests and the royal court of Judah were exiled to Babylon, where the idea of Yahweh as the only God took birth. Today, this idea of Yahweh/Elohim (different names for the same God) is the most prominent, and the Hebrew Bible commands the Israelites to only worship the God of Jacob, Abraham, and Isaac, who got his followers out of Egypt. Also, Yahweh is believed to be the start and end of everything. Like Islam, Judaism also does not consider Christianity to be monotheistic, due to the divine status of Christ and the Trinity.
Islam originated in the 7th century, slightly influenced by Christianity and Judaism. At present, it is the 2nd largest religion in the world, with a following of around 1.6 billion people. The belief that this religion is based on, states that the religion brought by Prophet Muhammad is the same as that worshiped by prophets such as David, Jacob, Abraham, and many others. However, they also believe that the message of God has been corrupted and changed over the passage of time, and for this purpose, God sent the correct message to Muhammad through the Quran. In Islam, Allah is the one who creates, maintains, destroys, and judges everything in the universe. He is omnipotent, omniscient, and omnipresent. Islam believes Allah to be a unique being without start or end, one who consists of everything that is good, and will tolerate no evil. Although Jesus is mentioned many times in the Quran, he is not considered as the Son of God.
Christianity is the largest religion in the world, with an approximate following of 2.2 billion people. Originally a sect of Judaism, Christianity's monotheism is different, i.e., God the Father, Son, and the Holy Spirit define separate divine persona. However, both the New and the Old Testaments say that there is only one God, and that the Trinity are only different facets of the same God. Some Christian sects such as Mormonism believe that the Trinity are three different individuals who work together with separate purposes toward a common end for mankind.
This religion is widely thought to be the first to have a monotheistic belief. Sometime during the 16th to 8th century BC, Zarathustra, an Iranian prophet, turned away from the prevalent polytheistic practices of the region. He brought together the ideas of divinity from various religions into one being called Ahura Mazda, who is a just, righteous God, who creates all good things and works the world through six angels. However, the spheres of good and evil are controlled by two beings called Spenta Mainyu and Angra Mainyu, respectively, both who have been fathered by Ahura Mazda. Because of this, some do not consider Zoroastrianism to be purely monotheistic. Rather, it is considered to be a subtype, where a great God who represents good opposes the less powerful forces of evil.
In the Bahá'í Faith, the concept of God is believed to be too vast for the human mind to understand. The Bahá'í Faith does not agree with Christianity's view of the Holy Trinity, nor with Prophet Muhammad's revelations. To help humans to truly understand, God passes his revelations and laws through divine prophets, who are known as the manifestations of God. That God is a singular being is a major teaching in this religion. According to the faith, God is a being who was not created, nor can be destroyed. It is believed that all things in creation are to help man to better understand the image of the Creator.
Mukuru is the name of the God worshiped by the Himba and Herero people of Namibia. They believe that He is an all powerful deity who delivers life-giving rain, saves sick people, and that all people are His children. Death is believed to be Mukuru's call to his child to return home. They also believe that all deceased people serve Mukuru. The Herero people believe that their tribal chief is an incarnation of God, who works to complete Mukuru's earthly tasks.
The Igbo people of Nigeria consider Chukwu to be the Supreme Being. He is primarily made of five facets, i.e., Chukwu (Force that created all living beings), Okike (Creator of laws that govern every tangible and intangible thing in the universe), Agbala (Fertility of the all living beings and the spiritual dimension of the universe), Chi (Spiritual Guide), and Anyanwu (symbolic representation of the sun which is the origin of all knowledge in the universe).
The Oromo people who reside in parts of Ethiopia, Somalia, and Kenya, believe in a God named Waaq, who was prominent till Catholic missionaries attempted to convert the locals to Christianity, although he is still worshiped by some people in today's society. The concept of this religion explains that all of mankind are servants to Waaq, who have to live in constant fear of Him, and that they should always sing his praises. The God would get his bidding done by angels or spirits. The religion has a large prayer system, with long chants and rituals.
Most Chinese monarchies till the Shang Dynasty (1776 B.C.) followed the Shangdi system, which advocated that God or heaven was an all-powerful force. It described heaven as an entity without any particular form. Enormous shrines and temples were constructed, and emperors would regularly practice ritual sacrifices to Shangdi. Eventually though, the religion declined with the advent of Confucianism, Buddhism, and Taoism, and some of Shangdi's concepts were incorporated with modern religions.
Sikhism is a monotheistic religion that originated around the 17th century. The Sikh God Vaheguru (Waheguru, Vāhigurū) is an ethereal, timeless being, who is present in all of creation. The only way for man to see God is though the inner eye, which can be accomplished by gaining enlightenment through meditation. Sikhs believe that all other religions worship the same God, but call him by different names. Hindu and Islamic names such as Ram and Allah are mentioned in the Sikh holy texts.
Hinduism is the third largest religion in the world, with a following of around a billion people. Although it is widely known that Hinduism consists of millions of Gods and hundreds of sects, most religious leaders, and the holy scriptures (Vedas) say that even though God has a multitude of forms, and the ways to reach Him are also many, God is one. Any worship or ritual is ultimately to that one God (Brahman), who is the Creator, Protector, and Destroyer of all things.
Started by Pharaoh Amenhotep at around 1348 B.C., this religion initially supported the worship of other traditional Gods, with Aten as the head of the pantheon. Within a couple of years, the pharaoh changed his name to Akhenaten, as a symbol of his worship to Aten, and then built massive temples in his honor across ancient Egypt. By 1342 B.C., Akhenaten decreed Aten, not only to be the highest power, but also the only God to be worshiped, bringing a relatively unknown Sun God into prominence in Egypt's history. The people of the nation were to worship the pharaoh, while only Akhenaten and Nefertiti could worship the Sun God.
Around the 3rd century, oracles of Greek origin started advocating the idea that there is only one all powerful God, and that Gods from the polytheistic religions at the time were other forms of the same God. Others said that the Gods from the pantheon were servants to the Supreme God, who worked to do His bidding on the earth.
All the above religions have some major differences in their philosophy. However, there are enough striking similarities too, to show that they have been influenced by each other to a large degree. Because all these religions share the same goal of reaching that higher power, they have constantly intermingled and evolved together.