Although the teachings of prophet Zarathushtra were primarily spiritual, and
substantially devoid of mythological and ritualistic beliefs, Zoroastrianism, the religion
that was based on his teachings incorporated many aspects of pre-Zarathushtra traditions
as well as novel and creative approaches to ritualism.
When Zoroastrian conquerors and kings, primarily Cyrus the Great and his descendants
expanded the Persian Empire to include much of the known world at that time, inevitably
Zoroastrians encountered people of other faiths. While Cyrus true to Zarathushtra's
teachings, was very respectful of other beliefs and allowed them to flourish of their own
accord, and even supported them; it was inevitable that Zoroastrianism as the dominant
faith would influence the conquered peoples, perhaps more so than be influenced by them.
The priestly cast, namely the Magi, also did their utmost to influence other people and
guide them to the path of righteousness and Asha. After all, this was a moral duty, (see Ahuna Vairya prayer), to teach others about the path of Asha, and to show them the light of
Ahura Mazda, the Universal Divine.
In this exchange of thought and belief, what has obviously been transferred has been
some of the visibly manifest aspects of the religion, namely rituals and myths. This is
why when the influence of Zoroastrianism on Judaism and Christianity is studied, time and
again we return to:
The following extensively lists quotations from other scholars to emphasis the same
point, as well as to elaborate on many of these similarities. However, what is often
missed in these comparisons is the effect that such overwhelming influence would have on
shaping the faith, psyche and spiritual chemistry of the affected people. Namely, such
infiltration of mythology and ritualism will inevitably define a framework of what is
conceivable and possible vs. what was once inconceivable and consequently not part of the
world conception of that people. Let us first study some of these quotations::
  Frances Power Cobbe, Studies, new and
  old, of ethical and social subjects: 
  "Should we in a future world be permitted to hold high
  converse with the great departed, it may chance that in the Bactrian sage, who lived and
  taught almost before the dawn of history, we may find the spiritual patriarch, to whose
  lessons we have owed such a portion of our intellectual inheritance that we might hardly
  conceive what human belief would be now had Zarathushtra never existed."
   
  A.V. Williams Jackson, Zoroastrian Studies: 
  "The typical passage is found in the Hþtokht Nask (Yt. 22.
  1-36; and compares Vistþsp Yasht, Yt. 24. 53-64). For the first three nights after the
  breath has left the body the soul hovers about the lifeless frame and experiences joy or
  sorrow according to the deeds done in this life. On the dawn of the fourth day the soul
  takes fight from earth..." 
  Note: compare this to the crucifixion of Jesus on Good Friday,
  and his resurrection on Monday (the dawn of the fourth day). 
  "The author has attempted in his article in the Biblical
  World to show how much the Messiah-idea in Judaism and the Saoshyant-idea in Mazdaism,
  probably taught by Zarathushtra himself, resemble each other." 
  "The similarity between it (the Zoroastrian doctrine of the
  future life and the end of the world) and the Christian doctrine is striking and deserve
  more attention on the side of Christian theology, even though much has been written on
  this subject."
   
  Rustom Masani, Zoroastrianism: The
  Religion of the Good Life: 
  " `To all good thoughts, words, and deeds (belongs)
  Paradise, so is it manifest to the pure.' This is the simple admonition given in the
  prayer Vispa Humata."
   
  Joseph Campbell, The Hero with a
  thousand faces: 
  "Persian belief was reorganized by the prophet Zarathushtra
  according to a strict dualism of good and evil principles, light and dark, angels and
  devils. This crisis profoundly affected not only the Persians, but also the subject Hebrew
  beliefs, and thereby (centuries later) Christianity."
   
  James Henry Breasted, The Dawn of
  Consciousness: 
  P. 345
  "There is plenty of evidence that the post-exilic religious development of the
  Hebrews was affected by the teachings of Zarathushtra, and that among the international
  influences to which the development of Hebrew morals was exposed, we must include also the
  teachings of the great Medo-Persian Prophet." 
  P. 337
  "It was not until the rise of the Chaldean power (Neo-Babylonian) in the 6th century
  B.C. and the subsequent supremacy of the Persians after Cyrus, that the Babylonians
  disclosed outstanding intellectual interests and their noble astronomers laid the
  foundations upon which the astronomical sciences of the Greeks was later built up.
   
  John Gray, Near Eastern Mythology: 
  p. 16
  "The Persians had their own mythology, or rather their own conception of the natural
  and supernatural order, formulated by the religion of Zarathushtra. this cosmic
  philosophy, influenced by Babylonian astronomy, had an effect on late Jewish thought and
  Messianic expectations." 
  P. 127
  "The development of the concept of Satan as the personal power of evil, who had his
  counterpart in the archangel Michael, the champion of cause of man in God's purpose of
  creation, was probably developed under the influence of Persian Zoroastrian belief in the
  two conflicting spirits of good and evil...."
   
  Ninian Smart & Richard D. Hecht,
  Sacred texts of the world - A universal anthology: 
  "The (Zoroastrian) dualism between good and evil was to have
  an impact upon ancient Israel, Judaism, Christianity and Islam."
   
  R.C. Zaehner, The Dawn & Twilight
  of Zoroastrianism: 
  P. 20
  "Meanwhile in her encounters with the Medes and Persians, Israel had found a kindred
  monotheistic creed in the religion of Prophet Zarathushtra, and one of her own Prophets,
  Isaiah, did not hesitate to salute Cyrus, her liberator, as the Lord's anointed. From this
  religion too she learnt teachings concerning the afterlife altogether more congenial to
  her soul than had been the gloomy prospect offered her by her own tradition, teachings to
  which she had been a stranger before." 
  P. 51-52
  "An almost exact parallel to this solution of evil is to be found in the Manual of
  Discipline, perhaps the most interesting document of the Dead Sea sect of Qumran. That
  Judaism was deeply influenced by Zoroastrianism during and after the Babylonian captivity
  can scarcely be questioned, and the extraordinary likeness between the Dead Sea text and
  the Gathic conception of the nature and origin of evil, as we understand it, would seem to
  point to direct borrowing on the Jewish side."
  P. 57
  "Zarathushtra's doctrine of rewards and punishment, of an eternity of bliss and an
  eternity of woe allotted to good and evil men in another life beyond the grave is so
  strikingly similar to Christian teaching that we cannot fail to ask whether here at least
  there is not a direct influence at work. The answer is surely `Yes', for the similarities
  are so great and the historical context is so neatly apposite that it would be carrying
  skepticism altogether too far to refuse to draw the obvious conclusion." 
  P. 58
  "Thus from the moment the Jews first made contact with the Iranians they took over
  the typical Zoroastrian doctrine of an individual afterlife in which rewards are to be
  enjoyed and punishments endured. This Zoroastrian hope gained ever surer ground during the
  inter-testamentary period, and by the time of Christ it was upheld by the Pharisees, whose
  very name some scholars have interpreted as meaning `Persian', that is, the sect most open
  to Persian influence."
  P. 171
  "One is tempted to say that all that was vital in Zarathushtra's message passed into
  Christianity through the Jewish exiles." 
  P. 172
  "It is impossible to revive a religion once the well-springs of the original
  revelation have been allowed to dry up, and once the sacred language itself has become so
  sacred that it is no longer understood even by those who set themselves up as its official
  interpreters." 
   
  Paul William Roberts, In Search of the
  birth of Jesus - The Real Journey of the Magi: 
  "Without Zarathushtra there would be no Christ. He was the
  bridge, and the Romans burnt it...."
   
  Leo Trepp, A History of the Jewish
  Experience 
  P. 54
  "How did the idea of two opposing forces (Satan & God) originate? It too is the
  result of conditions during the Hellenistic age, a period when ideas were exchanged widely
  among various religions and nations. The principle of dualism came from Zoroastrianism,
  .... This idea spread through the wide open Hellenistic world; the controversy between God
  and Satan is its reflection in Judaism." 
  P. 55
  "....The people have a heavenly representative, a guardian angel. This is a new
  concept of Zoroastrian origin. Previously the term `Malakh', angel, simply meant messenger
  of God."
   
  John R. Hinnells, Persian Mythology 
  "It is thought by many that this doctrine `Zoroastrianism'
  was a source of influence for both Eastern and Western beliefs - Hinduism and Buddhism in
  the East, and Judaism and Christianity in the West."
   
As mentioned earlier, while it is obvious that such influence had considerably affected
the recipients culturally, the more overwhelming and significant influence is often
overlooked.
Zoroastrianism, through its cultural and socio-political influence carried the seed of
a world conception that was previously non-existent and even inconceivable to the affected
people, namely the existence of a monotheistic divinity, which is all good, and all light.
A divinity who created a dualistic physicality which for its very existence required dual
aspects, for each aspect is only definable and may be experienced in the full context of
itself vs. its opposite. And finally a conception that gives our lives purpose and
meaning, namely being progressive and working for the Good.
Effectively, this Zoroastrian influence generated a major paradigm shift in the
people's thoughts at that time and for generations since. It is therefore quite
justifiable to claim that Zarathushtra's world conception and teachings have affected the
Western thought and civilization both directly and indirectly.
The following is a list of some articles on the Internet on this subject.