Shai Secunda is a Mandel fellow at the Scholion Center for Interdisciplinary Jewish Research, and a lecturer in the Talmud department at Hebrew University.  He blogs at the Talmud Blog, which he founded and now co-edits.

The great contemporary scholar of religion Jonathan Z. Smith once remarked that the omnipresent substructure of human thought lies in the human capacity to make comparisons.  In ancient Sumer, scribes crafted intricate similes.  In classical Greece philosophers discussed and employed the critical tools of analogy and metaphor.  And following the European Enlightenment, university professors made their contribution by inventing the field we know today as "comparative religion."  From the field's earliest days, Zoroastrianism—the ancient dualistic religion of Iran, whose adherents worshiped Ahura Mazda ("Lord Wisdom") and his heavenly hosts and battled the evil Angra Mainyu ("Foul Spirit") and his demonic minions—has played a central role in the way the modern academy has studied the religions of the world.

The existence of Zoroastrianism was known in the West for centuries.  The religious figure Zoroaster and the Persian religion appeared in classical Greek sources; Zoroastrianism, in the persons of the magi, even made a cameo appearance in the New Testament.  But, as of the beginning of the Enlightenment, neither Zoroastrianism's sacred texts nor the practices and beliefs of Zoroastrians actually living in Iran and the Indian subcontinent were known to Western tradition.  Thus, Zoroastrianism was surrounded by an aura of mystery.  It was seen as a quintessential "natural" religion, evidence that a spontaneous religious apprehension of the world was common to all human beings.  Its delicious concoction of the known and the unknown sparked the imaginations of European scholars—including the 18th-century orientalist Thomas Hyde, whose efforts brought increased numbers of Zoroastrian texts to the West—and of 19th-century philosophers and poets from Nietzsche to Wordsworth. 

Religious scholars like Hyde were moved by the pressing need they felt to locate Zoroastrianism within the salvation history of Christianity.  Soon, however, Christian apologetics gave way to a more detached critique as intellectual heavyweights like Voltaire joined the discussion.  Indeed, Voltaire pointed to the autonomy of Zoroastrianism and its distance from the Christian tradition as evidence that the church did not have a monopoly on divine truth.  In this way, the existence of Zoroastrianism functioned as an important piece of the dialogue of secularization, the process that led to the modern critical study of comparative religions.

Jews had their own "Zoroastrian moment" during the Jewish Enlightenment, or Haskalah, of the late 18th and early 19th centuries.  There were solid academic reasons for the "enlightened" Jewish scholars known as maskilim to familiarize themselves with the research on Persian language, culture, and religion that was then emerging from the great European universities.  One reason was the importance of the so-called "Persian Period," a critical epoch in Jewish history.  Following the conquest of the Near East by the Persian ruler Cyrus in the 6th century B.C.E., Jews living in the land of Israel and in exile in Mesopotamia came under a Persian dominion that lasted for centuries.  Except for a brief interlude following the conquests by Alexander the Great in the 4th century B.C.E., Babylonian Jews were subjects of successive Iranian dynasties that together made up more than a millennium. 

A number of important books of the Bible were written during this period.  They reflect the Persian context, which appears most explicitly in the strange and rich tapestry that is the Scroll of Esther.  Moreover, the central work in the Jewish canon, the Babylonian Talmud, was produced in a location close to the ruling Iranian dynasty's winter capital of Ctesiphon; it contains many Persian "loanwords" and numerous references to Iranian kings, Zoroastrian religious leaders, and aspects of cultural and religious life in Iranian-ruled Mesopotamia. 

In addition, major Jewish beliefs that seem to have developed largely in post-biblical times, such as those concerning the afterlife, angelology, and the Messiah, bear striking resemblances to ancient ideas found in Zoroastrianism. 

All these connections encouraged Jewish scholars to learn Persian, read Zoroastrian texts, and engage in a sustained comparative endeavor.  Their project engaged some of the most prominent figures of the era.  The Hungarian maskil Alexander Kohut, who (among his other accomplishments) edited and vastly expanded the classic 11th-century talmudic dictionary, the Arukh, and filled it with Persian etymologies, was fascinated by the world of Zoroastrian angelology and demonology and charted many correspondences between the Persian system and its Jewish counterpart.

But some of the most interesting Jewish writing on Zoroastrianism occurred on the fault line between Jewish apologists and anti-Orthodox crusaders.  The Austrian talmudist Isaac Hirsch Weiss was drawn to parallels between Zoroastrianism and the Talmud; he listed a number of critical areas in which, he argued, the rabbis had adopted Persian practices.  Just as interesting, in other places Weiss claimed to have found signs of resistance—instances in which rabbis established practices specifically as a means of precluding certain "Persianisms" in practice and interpretation.  Perhaps the most radical and colorful character involved in the exploration of Zoroastrianism was a sharp-tongued Galician maskil named Joshua Heschel Schorr.  Like Voltaire, Schorr wanted to reform his religion radically by subjecting it to the rules of logic and a rationalistic approach.  Unlike the early modern Christians who treated Zoroastrianism, however, Schorr did not see in the ancient Iranian tradition an admirable "natural" religion or otherwise sagacious philosophical system.  In Schorr's orientalism, the Zoroastrian "Bible," or Avesta, was filled with strange and preposterous superstitions.  Any parallel he found between the Avesta and the Bible or Talmud was a sign of corruption in the latter and a reason for excision and reform.

In the 20th century, Jewish scholars continued to work on Zoroastrianism from a comparative perspective—but no longer with the same sense of theological urgency.  Along with their Christian colleagues, Jewish academics came to operate within a more "objective" context, which had moved on to other battles and had a concern with Zoroastrianism that was ostensibly free of direct theological concerns.  Nevertheless, now as then, there is no escaping the broader implications of research, even when it is conducted in the ivory tower of academic religious studies.  Every comparison contains the seeds of judgment; every comparative act has the potential to become an explosive affair.