Nor is there in Varuna any religious grandeur which, so far as it exceeds that of other divinities, is not evolved from his old physical side.
One cannot personify heaven and write a descriptive poem about him without becoming elevated in style, as compared with the tone of one that praises a rain-cloud or even the more confined personality of the sun.

There is a stylistic but not a metaphysical descent from this earlier period in the 'lords of the atmosphere,' for, as we shall show, the elevation of Indra and Agni denotes a philosophical conception yet more advanced than the almost monotheistic greatness attained by Varuna.

But one must find the background to this earlier period; and in it Varuna is not monotheistic.

He is the covering sky united with the sun, or he whose covering is rain and dew.

Indra treats Varuna as Savitar treats Mitra, supplants him; and for the same reason, because each represents the same priestly philosophy.
In the one extant hymn to Mitra (who is Indo-Iranian) it is Mitra that 'watches men,' and 'bears earth and heaven.' He is here (iii.