All things including human life, had no physical form. Everything was pure and without evil. Ahura Mazda asked the fravashis if he should give them physical form. He warned that if he did so they would no longer be perfect. Evil would enter the creation.
If it did so they would have to fight a long and hard battle to defeat it. The fravashis, however, wanted physical bodies. With physical form they would be free to act rather than remain forever in a state of inaction. In return for physical being they would fight Evil. Ahura Mazda brought the physical, or Getig, world into being. As he had warned, with it came evil in the form of Angra Mainyu, or Ahriman, who would bring imperfection, sin, evil, and death into the world. Ahura Mazda then set the holy spirit, Spenta Mainyu, the Truth, to guide the fravashis and to lead the battle against Angra Mainyu, the Lie.
With the twin spirits, Truth and the Lie, the world entered a stage called Gumezishn, the Mixture. This is the stage in which people live today. Good and Bad, Truth and The Lie, both exist in the universe. These two can never agree and so they must fight each other for the souls of humankind. Humans must fight evil in their hearts and minds. This they do with the help of Spenta Mainyu, the holy spirit of Ahura Mazda, and the Beneficent Immortals.
By living ethical lives and following the path of Asha people participate in the battle against Ahriman. Their good actions help to bring about the destruction of evil. Toward the end of this Gumezishn stage, three saviors will be born one thousand years apart. They will lead the righteous in the final battle against evil.