To breathe life in.
Mythology is stories about us. Stories about our hopes, dreams, fears, desires, needs, lusts, growth pains, final days, temptations, fantasies, nature's rules, career choices (god, king, one breasted amazonian warrior, woodsman) all tied up in a connected poetry that ponders why we do what we do.
And often someone's fact will be someone's fiction...
That is why each culture has it's revered myths, and sometimes, confuse them with reality, and try to make everyone think the same stories they do... and that doesn't work out well. They have forgotten that they are just stories. But I love the powerful imagery and love to mix it up.