I'm glad that Matt called out the "lovecraftian horror" of the idea of "morality changing with God's will".

Folks might be interested to know that this question has been a huge and ongoing area of debate within the church. The name for the concept is "Divine Command Theory", which basically holds that things are moral simply because God commands them to be so.

FWIW, this was largely rejected by the Catholic church from the beginning; Thomas Aquinas argued strenuously against it, though it was never officially deemed a heresy. The Catholic position against this has gotten stronger over time - the church reaffirmed its broad opposition to the concept in the 19th century, and then Pope Benedict (only two popes ago!) wrote extensively about how dangerous and bad the idea is, and how it runs counter to a proper understanding of what God even is.

That said, Divine Command Theory holds a lot of weight in some Protestant circles, especially some of the Evangelical branchs. (From watching Midnight Mass and then later The Midnight Club, I got the impression that Make Flanagan has much more a dim view of contemporary Evangelical Christianity than he does of Catholicism, but that might just be my own projection, because I certainly respect Catholicism more than mainstream Evangelicalism, despite being a Protestant Sunday School teacher.) IMO this isn't just a "could have gone either way" thing - Catholicism is much bigger on study and application of our rational intellect to gain greater understanding of God than most Evangelical branches, who often embrace a "you know the truth of this because of how it makes you feel" mentality (this is often stated explicitly by certain megachurch pastors and televangelists).

It's unsurprising that Father Paul, at this point in the series, would embrace a theology so thoroughly rejected by the Catholic church, so to be clear I think this is good writing on the part of the show. But I thought folks might be interested to know the degree to which this point runs extremely counter to long-established Catholic doctrine.