So I've been reading for weeks and I've found nothing on what I personally see as the primary message in the show! The fact that stereotypes and mental health have a close link and to not take everything at face value. Think about it, lucifer (the devil😈) isnt evil despite history portraying him as evil incarnate, and how much that stereotype affects lucifer emotionally (and physically since Angel's 'self actualise'). Yes it's a TV show, and yes it's just for entertainment but it, like most shows, has an overarching message for society, and that is to care more about our own and others mental health, to care about those we love and help if they are going through problems.
That's all, just care😊