The Gathas, consist of seventeen hymns composed by the great poet-prophet Zarathushtra around 1200 BC. They are arranged into five groups based on their meter:
The importance of the Gathas to Zoroastrianism cannot be emphasized enough. They are the centerpiece of scripture and inspiration, like the Tao Te Ching is to Taoism. The Gathas are also quite enigmatic and obscure, and other scriptures contain lengthy commentaries. As Helmut Humbach notes, "Zarathushtra did not compose the Gathas to teach people, but to invoke and glorify Ahura Mazda in a predominantly psalmodic way, very far from any dogmatic systematizing" (Gathas I, 1991, pg. 81.). Thus we must look to the rest of scripture for help in understanding both the Gathas and Zarathushtras teachings in general.
The Gathas are also filled with word plays and deliberate ambiguities, and they were likely intended to be used by initiates as meditative instruments to enlightenment (ibid pg. 86-7). As an example of the incredible sophistication of the Gathas, see Prof. Martin Schwartz' analysis of the parallel clusters of lexic, semantic, and phonic data which occur in concentric rings ('Sound, sense, and "seeing" in Zoroaster: The outer reaches of orality', in K.R. Cama Oriental Institute International Congress Proceedings, 1989, pp. 127 ff.).
According to Mary Boyce, "their poetic form is a very ancient one, which has been traced back (through Norse parallels) to Indo-European times. It seems to have been linked with a mantic tradition, that is, to have been cultivated by priestly seers who sought to express in lofty words their personal apprehension of the divine; and it is marked by subtleties of allusion, and great richness and complexity of style. Such poetry can only have been fully understood by the learned; and since Zoroaster believed that he had been entrusted by God with a message for all mankind, he must also have preached again and again in plain words to ordinary people." - Zoroastrians, Their religious beliefs and practices, London, 1979, pg 17.
In spite of the obscurities, the main messages of the Gathas seem fairly
clear: The struggle between good and evil, people of truth (ashavans) who
worship Ahura Mazda, struggling against the people of the lie (drugvants),
who worship the daevas. The benevolence /friendship of Ahura Mazda, the
importance of Asha, Vohu Mano, etc. Need for support by those who
manage/raise livestock, against those who disrupt their labors by looting
what they want. Importance for future reward. The reciprocal
relationship/partnership with Ahura, importance of offerings (draonah),
fire, ritual, and manthra. We also get very sketchy glimpses of their society
(household, district, etc.) and judicial system including ordeal, etc.