Zoroastrianism, or more natively Mazdayasna, is one of the world's oldest religions, "combining a cosmogonic dualism and eschatological monotheism in a manner unique... among the major religions of the world." Ascribed to the teachings of the Iranian Prophet Zoroaster (or Zarathustra), he exalted their deity of wisdom, Ahura Mazda, (Wise Lord) as its Supreme Being. Leading characteristics, such as messianism, heaven and hell, and free will are said to have influenced other religious systems, including Second Temple Judaism, Gnosticism, Christianity, and Islam. With possible roots dating back to the second millennium BCE, Zoroastrianism enters recorded history in the 5th-century BCE, and including a Mithraic Median prototype and Zurvanist Sassanid successor it served as the state religion of the pre-Islamic Iranian empires from around 600 BCE to 650 CE. Zoroastrianism has no major theological divisions, though it is not uniform; modern-era influences having a significant impact on individual and local beliefs, practices, values and vocabulary, sometimes merging with tradition and in other cases displacing it. In Zoroastrianism, the purpose in life is to "be among those who renew the world...to make the world progress towards perfection." Its basic maxims include: Humata, Hukhta, Huvarshta, which mean: Good Thoughts, Good Words, Good Deeds. There is only one path and that is the path of Truth. Do the right thing because it is the right thing to do, and then all beneficial rewards will come to you also. The most important texts of the religion are those of the Avesta, which includes the writings of Zoroaster known as the Gathas, presented here in this book which are enigmatic poems that define the religion's precepts, and the Yasna, the scripture. The full name by which Zoroaster addressed the deity is: Ahura, The Lord Creator, and Mazda, Supremely Wise. He proclaimed that there is only one God, the singularly creative and sustaining force of the Universe. He also stated that human beings are given a right of choice, and because of cause and effect are also responsible for the consequences of their choices. Zoroaster's teachings focused on responsibility, and did not introduce a devil, per se. The contesting force to Ahura Mazda was called Angra Mainyu, or angry spirit. Post-Zoroastrian scripture introduced the concept of Ahriman, the Devil, which was effectively a personification of Angra Mainyu. Included in this interpretation of the book is a list of Glossary terms for the reader to further understand one of the oldest religions in the world.

For the first time, the vowels of Avestan are studied comprehensively on the synchronic and diachronic level. All vowel changes which have occurred after the Proto-Iranian stage are discussed, and they are placed in a relative chronology. The phonological system of Avestan at various stages of its development is reconstructed, and the relationship between Old Avestan and Young Avestan is reviewed. Also, many philological details are discussed. This volume is of interest for Indo-Iranian philology, for Indo-European linguistics and for Iranian linguistics.

Zarathusthtra brought about important religious reform in Iran, giving a definitely moral character and direction to religion whilst at the same time preaching the doctrine of monotheism, which offered an eternal foundation of reality to goodness as an ideal of perfection. This volume provides a substantial introduction on the life and doctrines of Zarathushtra and compares the development of religion in India with that of Iran.

The Zend-Avesta is the sacred book of the Parsis, that is to say, of the few remaining followers of that religion which feigned over Persia at the time when the second successor of Mohammed overthrew the Sassanian dynasty, and which has been called Dualism, or Mazdeism, or Magism, or Zoroastrianism, or Fire-worship, according as its main tenet, or its supreme God, or its priests, or its supposed founder, or its apparent object of worship has been most kept in view. In less than a century after their defeat, nearly all the conquered people were brought over to the faith of their new rulers, either by force, or policy, or the attractive power of a simpler form of creed. But many of those who clung to the faith of their fathers, went and sought abroad for a new home, where they might freely worship their old gods, say their old prayers, and perform their old rites. That home they found at last among the tolerant Hindus, on the western coast of India and in the peninsula of Guzerat. There they throve and there they live still, while the ranks of their co-religionists in Persia are daily thinning and dwindling away. As the Parsis are the ruins of a people, so are their sacred books the ruins of a religion. There has been no other great belief in the world that ever left such poor and meagre monuments of its past splendour. Yet great is the value which that small book, the Avesta, and the belief of that scanty people, the Parsis, have in the eyes of the historian and theologist, as they present to us the last reflex of the ideas which prevailed in Iran during the five centuries which preceded and the seven which followed the birth of Christ, a period which gave to the world the Gospels, the Talmud, and the Qur’ân. Persia, it is known, had much influence on each of the movements which produced, or proceeded from, those three books; she lent much to the first heresiarchs, much to the Rabbis, much to Mohammed. By help of the Parsi religion and the Avesta, we are enabled to go back to the very heart of that most momentous period in the history of religious thought, which saw the blending of the Aryan mind with the Semitic, and thus opened the second stage of Aryan thought.