The groundbreaking contribution to religious and spiritual thought in the Rig Veda is the idea that the ultimate Existence or Truth is ‘One’ and can be described variously by wise people: ‘ekam sat viprah bahudha vadanti; the truth is one and the sages call it variously.’ (Rig Veda, 1.164.46.)
Even today when bitter struggles rage over the superiority of one God of a particular religion over another, the Vedic sages were able to express the nature of this ultimate reality in an abstract manner calling it just Existence or Truth. It is not only that the ultimate reality does not have a single name but it is also not defined by any gender; this is an intellectual feat of the highest order in any time and age.
In the early Vedic age both female and male deities enjoyed the same status. This attitude was facilitated by the open ended way of looking at religion, which enabled the Vedic sages to view the entire cosmos as endowed with divinity. Thus everything in the universe was imbued with the presence of the divine and the question of distinguishing the female from the male or according superiority to one over the other would not fit into the overall scheme of Vedic philosophy.
This tendency would later blossom into the concepts of Brahman and Atman in the Upanishads where the outer reality Brahman got to be identified with the inner reality in everything that exists called Atman. It is also echoed in the Ardhanarishvara concept where Shiva is viewed as half male and half female emphasizing the importance of both male and female in Nature.
Source - Excerpts from article titled 'Shakti, the Supreme:Mother Goddess in Hinduism' by T S Rukmani in Prabuddha Bharata January 2016 edition (page 89 - 90).