Comparative religion is the branch of the study of religions concerned with the systematic comparison of the doctrines and practices, themes and impacts (including migration) of the world's religions. In general the comparative study of religion yields a deeper understanding of the fundamental philosophical concerns of religion such as ethics, metaphysics and the nature and forms of salvation. Studying such material facilitates a broadened and more sophisticated understanding of human beliefs and practices regarding the sacred, numinous, spiritual and divine.
In the field of comparative religion, a common geographical classification of the main world religions distinguishes groups such as Middle Eastern religions (including Iranian religions), Indian religions, East Asian religions, African religions, American religions, Oceanic religions, and classical Hellenistic religions.
There also exist various sociological classifications of religious movements.
Al-Biruni and Ibn Hazm of the Islamic Golden Age compared the study of religious pluralism and their works have been significant in the fields of theology and philosophy. Social scientists in the 19th century took a strong interest in comparative and "primitive" religion through the work of Max Müller, Edward Burnett Tylor, William Robertson Smith, James George Frazer, Émile Durkheim, Max Weber, and Rudolf Otto. Nicholas de Lange, Professor of Hebrew and Jewish Studies at Cambridge University, says that
The comparative study of religions is an academic discipline which has been developed within Christian theology faculties, and it has a tendency to force widely differing phenomena into a kind of strait-jacket cut to a Christian pattern. The problem is not only that other 'religions' may have little or nothing to say about questions which are of burning importance for Christianity, but that they may not even see themselves as religions in precisely the same way in which Christianity sees itself as a religion.
In the study of comparative religion, the category of Abrahamic religions consists of the three monotheistic religions, Christianity, Islam and Judaism, which claim Abraham (Hebrew Avraham ; Arabic Ibrahim ? ) as a part of their sacred history. Smaller religions such as Bahá'í Faith that fit this description are sometimes included but are often omitted.
The original belief in the God of Abraham eventually became strictly monotheistic present-day Rabbinic Judaism. Judaism is considered by religious Jews to be the expression of the covenant that God established with the Children of Israel. Jews hold that the Torah is part of the larger text known as the Tanakh or the Hebrew Bible, they also believe in a supplemental oral tradition represented by later texts such as the Midrash and the Talmud.
Christians believe that Christianity is the fulfillment and continuation of the Jewish Old Testament. Christians believe that Jesus (Hebrew Yeshua ) is the awaited Messiah (Christ) foretold in the Old Testament prophecies, and believe in subsequent New Testament scripture. Christians in general believe in that Jesus is the incarnation or Son of God. Their creeds generally hold in common that the incarnation, ministry, suffering, death on the cross, and resurrection of Jesus was for the salvation of mankind.
Islam believes the present Christian and Jewish scriptures have been corrupted over time and are no longer the original divine revelations as given to the Jewish people and to Moses, Jesus, and other prophets. For Muslims, the Quran is the final, complete revelation from God (Arabic ? Allah), who believe it to have been revealed to Muhammad alone, who is believed by Muslims to be the final prophet of Islam, and the Khatam an-Nabiyyin, meaning the last of the prophets ever sent by Allah ("seal of the prophets").
Based on the Muslim figure of the Mahd?, the ultimate savior of humankind and the final Im?m of the Twelve Imams, Ali Muhammad Shirazi, later known as Bab, created the Bábí movement out of the belief that he was the gate to the Twelfth Im?m. This signaled a break with Islam and started a new religious system, Bábism. However, in the 1860s a split occurred after which the vast majority of Bábís who considered Mirza Husayn `Ali or Bahá'u'lláh to be Báb's spiritual successor founded the Bahá'í Movement, while the minority who followed Subh-i-Azal came to be called Azalis. The Bahá'í division eventually became a full-fledged religion of its own, the Bahá'í Faith. In comparison to the other Abrahamic religions, Judaism, Christianity and Islam, the number of adherents for Bahá'í faith and other minor Abrahamic religions are not very significant.
Out of the three major Abrahamic faiths, Christianity and Judaism are the two religions that diverge the most in theology and practice.
The historical interaction of Islam and Judaism started in the 7th century CE with the origin and spread of Islam. There are many common aspects between Islam and Judaism, and as Islam developed, it gradually became the major religion closest to Judaism. As opposed to Christianity, which originated from interaction between ancient Greek, Roman, and Hebrew cultures, Judaism is very similar to Islam in its fundamental religious outlook, structure, jurisprudence and practice. There are many traditions within Islam originating from traditions within the Hebrew Bible or from post-biblical Jewish traditions. These practices are known collectively as the Isra'iliyat.
The historical interaction between Christianity and Islam connects fundamental ideas in Christianity with similar ones in Islam. Islam accepts many aspects of Christianity as part of its faith – with some differences in interpretation – and rejects other aspects. Islam believes the Quran is the final revelation from God and a completion of all previous revelations, including the Bible.
Several important religions and religious movements originated in Greater Iran, that is, among speakers of various Iranian languages. They include Mithraism, Ætsæg Din, Yazdanism, Ahl-e Haqq, Zurvanism, Mandaeism, Manichaeism, and Mazdakism.
In comparative religion, Indian religions consists of all the religions that originated in South Asia. It is thought that "the kinship of the religions of India stems from the fact that Jains, Buddhists and Sikhs look back to Hinduism as their common mother."
Al-Biruni deeply studied the Vedic religions and through his works essential details about pre-11th century India's religions and cultures were found. Adi Shankaracharya was an early 8th century philosopher and theologian who consolidated the doctrine of Advaita Vedanta.[note 1] Gautama Buddha is mentioned as an Avatar of Vishnu in the Puranic texts of Hinduism. Most Hindus believe the Buddha accepted and incorporated many tenets of Hinduism in his doctrine. Prominent modern Hindu reformers such as Mahatma Gandhi and Vivekananda acknowledge Buddhist influence. Gandhi, like Hindus himself did not believe Buddha established a non-Hindu tradition. He writes, "I do not regard Jainism or Buddhism as separate from Hinduism."
A Taoic religion is a religion, or religious philosophy, that focuses on the East Asian concept of Tao ("The Way"). This forms a large group of eastern religions including Taoism, Confucianism, Jeung San Do, Shintoism, I-Kuan Tao, Chondogyo, and Chen Tao. In large parts of East Asia, Buddhism has taken on some taoic features.
Tao can be roughly stated to be the flow of the universe, or the force behind the natural order. It is believed to be the influence that keeps the universe balanced and ordered and is associated with nature, due to a belief that nature demonstrates the Tao. The flow of Ch'i, as the essential energy of action and existence, is compared to the universal order of Tao. Following the Tao is also associated with a "proper" attitude, morality and lifestyle. This is intimately tied to the complex concept of De, or literally "virtue" or "power." De is the active expression of Tao.
Taoism and Ch'an Buddhism for centuries had a mutual influence on each other in China, Japan, Korea, and Taiwan. These influences were inherited by Zen Buddhism when Ch'an Buddhism arrived in Japan and adapted as Zen Buddhism.