I’m not clear what you mean when you say that myths are accepted on faith. Myths, to my experience, are in a category of their own. They are stories that turn the mind away from the objective and back to the subjective so we can see ourselves and thereby find a way to solve our own problems thanks to their guidance through metaphor, archetypes, and story.
Is the fact that humans “aren’t just animals” the basis of why we may be said to have a purpose?
Ironically, it is only the human being who claims that human beings have a purpose, while the rest of creation goes along existing without such self-aggrandizing ideas. Because humans have the power to envision and rationalize doesn’t mean that they have a personal purpose.
When we entertain whether our lives, actions, thoughts, and achievements have a point then we enter into rationalization and the insertion of the ego so that it may proclaim that it is superior and important. If we were to remove the ego from the equation then there would be no one to judge any action or effort to be pointless, purposeful, meaningful, enriching, deleterious, or important. There would only be action brought about by the forces that actually underlie the sense of self.
Of course we can go too far with this business of purpose. Religious adherents, for instance, rationalize that our purpose is to serve God and they have a whole geschicht telling us why this is so. But this is belief, and belief has no gravitas except to the believer and other likeminded believers.
What if we were able to abandon the ego, the sense of self, so that we would be unaffected by its inculcations, ideas, memories, psychological conditioning, beliefs, and philosophies? What, then, would be left to judge, criticize, or claim anything about a purpose to life? If the self is an illusion or construct as so many neuroscientists, philosophers, and mystics have claimed, then so are ideas of importance and purpose. Only the self has such ideas, and we always have to question the self's reasons for everything it is inclined to believe, imagine, or proclaim.