One of the greatness of Hinduism is that God is not defined by any gender in Hindu religion. Vedic sages express the nature of God not as male or female but in an abstract manner calling it just Existence or Truth. God is not man. God is not woman. God is Truth. ‘Ekam sat viprah bahudha vadanti; the truth is one the wise call it by different names.’ (Rig Veda, 1.164.46.)
We thus find that the hymns in Vedas dedicated to female deities like Vak, Ushas, or Ratri were no less important than the ones dedicated to male deities. It is also significant that the Kena Upanishad mentions a female goddess Uma Haimavati as the one who instructs Indra about Brahman.
All these examples make it clear that 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.
The absence of defining the ultimate in terms of gender allowed for a freedom to conceptualise the reality in many ways without a gender bias. For instance the Shvetashvatara Upanishad describes the ultimate reality in the following manner: ‘You are the woman, you are the man, you are the boy, (and) you are the girl too. You are the old man tottering with a stick. Taking birth, you have your faces everywhere.’ It is also significant that in the Bhagavad Gita Sri Krishna declares: ‘Of this world I am the father, mother, ordainer, (and the) grandfather.’
It is later in the tantra literature and the many Puranas which are dedicated to Shakti worship that this tradition reaches its culmination. In these works Shakti is the supreme deity responsible for the manifestation, maintenance, and destruction of the universe. Moreover she is not depicted as the consort of one of the male divinities but is independent and is supreme in her own right.
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).