When the circle is narrowed to that of the Indo-Iranian connection the similarity in religion between the Veda and Avesta becomes much more striking than in any other group, as has been shown.  It is here that the greatest discrepancy in opinion obtains among modern scholars.  Some are inclined to refer all that smacks of Persia to a remote period of Indo-Iranian unity, and, in consequence, to connect all tokens of contact with the west with far-away regions out of India.  It is scarcely possible that such can be the case.  But, on the other hand, it is unhistorical to connect, as do some scholars, the worship of soma and Varuna with a remote period of unity, and then with a jump to admit a close connection between Veda and Avesta in the Vedic period.  The Vedic Aryans appear to have lived, so to speak, hand in glove with the Iranians for a period long enough for the latter to share in that advance of Varuna-worship from polytheism to quasi-monotheism which is seen in the Rig Veda.  This worship of Varuna as a superior god, with his former equals ranged under him in a group, chiefly obtains in that family (be it of priest or tribe, or be the two essentially one from a religious point of view) which has least to do with pure soma-worship, the inherited Indo-Iranian cult; and the Persian Ahura, with the six spiritualized equivalents of the old Vedic [=A]dityas, can have come into existence only as a direct transformation of the latter cult, which in turn is later than the cult that developed in one direction as chief of gods a Zeus; in another, a Bhaga; in a third, an Odin.  On the other hand, in the gradual change in India of Iranic gods to devils, asuras, there is an exact counterpart to the Iranian change of meaning from deva to daeva.  But if this be the connection, it is impossible to assume a long break between India and the west, and then such a sudden tie as is indicated by the allusions in the Rig Veda to the Persians and other western lands.  The most reasonable view, therefore, appears to be that the Vedic and Iranian Aryans were for a long time in contact, that the contact began to cease as the two peoples separated to east and west, but that after the two peoples separated communication was sporadically kept up between them by individuals in the way of trade or otherwise.  This explains the still surviving relationship as it is found in later hymns and in thank-offerings apparently involving Iranian personages.

They that believe in a monotheistic Varuna-cult preceding the Vedic polytheism must then ignore the following facts:  The Slavic equivalent of Bhaga and the Teutonic equivalent of V[=a]ta are to these respective peoples their highest gods.  They had no Varuna.  Moreover, there is not the slightest proof that Ouranos in Greece[25] was ever a god worshipped as a great god before Zeus, nor is there any probability that to the Hindu Dyaus Pitar was ever a great god, in the sense that he ever had a special cult as supreme deity.