At its core it posits an unyielding and uncaring Universe with no external Moral Values imposed by supernatural forces.
No Heaven, no Hell, be as evil as you want and then you disappear- star dust if that’s any solace.
But, but, but, without external discipline, why should we behave Morally at all?
Well, for one thing I don’t like the word ‘Moral’. I prefer ‘Ethical’. And by that I mean that I deliver what I promise and don’t deliberately look to cheat you or hurt you, the deal is the deal. Presumably we both win, you get what you want and I get what I want. And I’m not uncharitable, I’m a nice guy and if I can help you out I will. The cynical might call it an investment in future relationships which is true enough.
Does ‘Ethical’ behavior benefit you? Well, if you get the reputation for it, future transactions are easier to initiate and complete. People admire and look up to you as a pillar of the Community. You might even be called ‘Moral’ (ugh).
I’m very happy I’m not even Internet Famous anymore, it’s a heck of a thing to live up to.
So that’s Existentialism. Antidisestablishmentarianism is the belief that Britain should have an official Church headed by the Monarch.