God = a woman

Why do people think God is a man? Where did that come from, because when people talk of God they always use a male pronoun. 
Why is he not thought of as a woman? Woman can create life. Men can not. Nature is thought of as Mother Nature, seas/oceans are thought in a female pronoun like "her waters are rough and choppy today". Why is God thought of as a He? You would think the creator of the universe, which people base off a human life form, would actually be the human that can procreate.