You touched on it, but for completeness, the official Catholic stance is actually a pretty interesting interpretation that is the result of a kind of wild assumption, and the absolute upholding of free will. Basically God is meant to be the source of all positive things, including feeling and sensation. Every person has a 2 way connection to God. Any positive feeling you've ever had was from him through this connection. When someone commits a Mortal Sin, they are showing they reject God, and sever their side of the connection. Truly repenting will pick the line back up, and God never drops his side so long as you live. If you die with a severed line, he accepts that you really don't want to associate with him, and he drops his side too. And so Hell is not a place, nor a punishment, it's a state of being. All the gnashing of teeth and lakes of fire were originally metaphors for how badly a total lack of Grace, that connection, is. Later Dante's Inferno and other works painted it in a striking way that caught the imagination, but it is not the Church's official stance.

The really fun part is smashing together the idea that Mortal Sin is a rejection of God, and the core concept of the Silent Christian. IE, the Bible very literally, and repeatedly, states that God is love. Like, not that he embodies it, or that he is the source of it (though it also does claim that) but that the two concepts are literally interchangeable. You basically can rewrite it using a replace tool and swap out any instance of God, Jesus, or the Holy Ghost with Love. It does make some kind of philosophical strange abstractness when it talks about loving Love, not that weird, with Love loving things, pretty weird. And it kind of takes "tough love," to a whole new level with some of the wrath he brings in the 1st Testament, but that is fairly low on the list of weirdness between the two Testaments, and the God = love stuff is mostly from the 2nd.

But the core concept in the "invisible Christian," is that those with no faith in a sky daddy can still be good Christians by letting God love into their hearts. Therefore, anyone that has empathy can really be taken to be a good Chrostian, and obtain all the benefits whenever the Bible says you need to beleive in and accept God. And the corollary here is that committing Mortal Sin, IE willingly committing a heinous act such as murder, is a rejection of God love in your life. Of course, the definition of what qualifies as Mortal Sin remains a contentious affair. Though the Catholics are generally more tolerant than the more hard-line sects, they are still pretty backwards here. But if you restrict it to things that cause serious harm to another person, then it becomes a comparatively reasonable model. Much more so than it is popularly presented, at any rate.