Like I said several posts ago, a Demon might become Good, by following that exact path above, and it should be a strugle to finally achieve forgiveness and stop being a Demon. Ergo you can't have Good Demons or Evil Angels.
Or let me put it in a different way, fallen Angels already have a name, we call them Demons, likewise good "demons" already have a name, we call them angels. It's basic Theology my dude.
Part of the problem with drawing the parallel is that, at least in Catholic theology, angels can no longer fall and demons can no longer repent--the former because they now possess the Beatific Vision and are thus confirmed in goodness; the latter, because they made their choice with a complete understanding and full commitment of the will.
This is one of several reasons that I prefer to refer to the D&D creatures as 'fiends' and 'celestials'--they're too material, mutable, and weak for me to find them realistic representations of the real things.
True, but lets say you're a practicing Christian and want to write some fiction with a small amount of the real thing in it for verosimilitude and yet have those in your fiction, you would need to follow the path I delineated. Just to make it seem possible without going too deep into the Theology.
Yep. I suffer from the curse of the expert in this regard, but you can have works that are thematically solid while taking liberties with the details.
Same here, but I was trying to make it possible to have evil angels and good demons from thw word go, which is why I took only enough of the Theology to make it verosimil for the casual reader.
And it wopuld work perfectly in an RPG: Say you want to play a Tiefling, a Good one, well, since Tieflings (in my houserules) are born evil you'll need to go thru a redemption arch, not unlike to the redemption quest for a Paladin that strayed from the true path.
At the end of it, after strugling with your nature, if you succeed you'll become something else, an aasimar. Which will also change your powers of course.
I've only had the one player that wanted to play a Tiefling go thru, most refuse to play at my table or choose a different race. Which is fine with me since I dislike with a passion the special snowflake races.