Similarities to Other Religions
Zoroastrianism has often been noted for its similarity to the monotheistic religions of Judaism, Christianity and Islam. Like these three, it teaches belief in one god, a supreme force of good who is opposed by the ultimate force of evil. All these religions believe in a definite difference between good and evil — as opposed to several Eastern religions which generally believe that since all things are of God then good and evil are relative. There is also a spirit medium between God and humans: Spenta Mainyu in Zoroastrianism; the Holy Spirit and Jesus in Christianity; and the Angel Gabriel in Islam. Angels and demons also feature in all four of these religions.
The symbol of fire, an important Christian symbol of the Holy Spirit and everlasting life, is also important in Zoroastrianism for essentially the same reason: believed to be a perfect embodiment of Ahura Mazda, a flame is kept burning at all times in a temple. But then again, many religions stress the symbolic importance of fire — including Hinduism, a polytheistic faith. Finally, the belief that “one should not do to others anything that does not seem good to oneself" is also expressed in different words in the ethics of Judaism, Christianity and Islam.
However, there are also important differences. The three Abrahamic faiths believe that humans have free will to choose between good and evil, like Zoroastrianism. But while the Judeo-Christian tradition teaches that Satan was created by God and was good before he fell, Angra Mainyu is a deity of evil unto himself. Islam is also more strictly monotheistic than any of these religions, believing in angels only as messengers and rejecting the idea of intermediaries like Spenta Mainyu, Jesus or the Holy Spirit.
All in all, though, the similarities of these religions — especially their teachings of ethics and good deeds and their common origin in the Middle East — are more significant than their differences.