Part of the reason why William Peter Blatty considered The Ninth Configuration as a true sequel to The Exorcist is because they both attempt to address the “mystery of the good.”
Blatty, from my understanding of course, was a devout Catholic so he understood these terms from a very spiritual perspective. While I find the phenomenon of religion fascinating, I don’t view the universe in that particular way. Nevertheless, I think Blatty was attempting to address a very interesting question, particularly with The Ninth Configuration (the film. I haven’t read the novel)
Much ado is made about “the problem of evil”, but that’s only a problem from a religious perspective. If the the universe is indifferent to our plight, and life is inherently selfish, then there is no mystery. Furthermore, there is no good OR evil…it’s merely a projection of human perception.
Many philosophers have attempted to formulate a model for morality, notably Kant’s Categorical Imperative and utilitarianism, with varying degrees of success. I personally tend to favor something that I heard Bart Ehrman say: I just know it when I see it. However I do find it interesting that nearly every religion has some variant of the Golden Rule: do unto others as you’d have them do unto you.
I don’t think that I have many philosophical convictions, but one thing I am certain of is that I am not a “blank slatist”. If we were born as blank slates, then nothing we do would be possible. Language acquisition itself provides some insight into the a priori nature of our being. What language can tell us precisely about our morality is unknown to me, but I think it warrants further investigation as evidenced by the Golden Rule.
The Golden Rule may not be a “philosophically consistent” principle, but I think it’s intuitive enough that there could possibly be something revealing about it. Empathy might be an example. To my understanding, empathy is a phenomenon that’s scientifically falsifiable, but I’m just spitballing here. Maybe “good” and “evil” are a priori categories of human reasoning, I dunno.
Either way, from both a religious and secular perspective, “the problem of good” needs answering.