Zarathustra’s Gathas today count among 

the most difficult products of world literature. This is not merely because we  

are so remote from them. The conciseness of the wording, the ambiguity of the  

inflectional endings, the abundance of technical terms that do not recur even in  

the Younger Avesta, the apparent attempt to depict by means of the word order 

obscure sequences of thought, all these are factors which must have made the Gathas  

extremely difficult to understand at all times. In addition, it must be realized  

that there was a considerable language barrier between the ancient Persians and  

the speakers of the Avestan language. The difference between Median and Avestan 

must have been less great, but a difference undoubtedly existed.

 I said earlier in my class that Darius appears to have accepted the substance of Zarathustrianism. It is unlikely that much more than the main drift of this subtly balanced doctrine could have been apprehended by a foreigner, as Darius was in respect to Zarathustra. But if our reading of the relevant hints in the Darius inscriptions is correct, Darius understood the principles of the faith far better than anyone else in antiquity of whom we have any record, apart, of course, from Zarathustra himself. In any effort to inform himself of the message of the prophet, Darius would have been favored by an opportunity forever denied to those who after him endeavored to understand the Gathas: his chronological nearness to Zarathustra. In Darius ‘s youth and early manhood, at a mere two or three decades from the death of the prophet (v. Henning, Zoroaster, 41), the possibility still existed for Persians or Medes to have the Gathas explained to them by men who had known Zarathustra, provided that one of those concerned was bilingual. By the middle of the fifth century such opportunities had vanished, not only in Western Iran but also in the homeland of the scripture. Even the authors of the Younger A vesta, who must have known the text of the Gathas by heart, had only an imperfect understanding of their contents.

By the middle of the fifth century such opportunities had vanished,not only in Western Iran but also in the homeland of the scripture. Even the authorsof the Younger Avesta, who must have known the text of the Gathas by heart, had only an imperfect understanding of their contents.

See -The Pahlavi Yasna Of the Gathas. Malandra and Ichaporia