This final question is a kicker.  If the brain builds the mind does it even make any sense to talk about our lives having a specific purpose?  Well, actually, yes.  Every brain is individual, different brains engage in different things.  Finding and connecting with our life's purpose means giving our brains opportunities to engage in those activities they both enjoy and are good at.  When we are challenged by a task but have the skills to meet that challenge we experience a psychological state called flow.  It sees the brain focused and working hard  in pursuit of a singular goal, these moments when our sense of self dissolves and we are utterly engaged in the moment can be some of the happiest of our lives.