The one true god is the neutral Brahman, but it is not revered as it is not 'erotic' in the sense of Shiva, Shakti, Vishnu, Bhairava and all the other awesome forms that spawn from the great Brahman. Even the God Brahma is different from the Brahman, which has no face. It is only the "inherent rumbling" of the cosmos. So ultimately the Hindu Brahmans did most certainly believe in one Cause, and their considered it the holy work of man as the king of all nature to bring this Cause into Manifestation. In this, they created/werecreatedby, sustained and drew from the deities of manifestation, especially those of energy (Shakti) and Power (Shiva), whic together for the erotic form that gives India its wild, joyful nature.