I think the "ain't no angel like you and Jenny here" fits in with the examples I gave. I, at least, would leave out the Twist ranch scene (or maybe discuss it in a different sort of discussion of religion). ... First he's a part of it, and feels as his attraction to Jack is a sin. Then he withdraws from it, partly hinting that there's something wrong with him ("I ain't no angel"), but also partly hinting that there's something wrong with society ("that fire-and-brimstone crowd"). And then with his daughter's wedding, he's simply going to participate -- there aren't any references to sin or guilt. But he's going to be part of the community, in some sort of way.
I can't speak to Christian symbolism at the Twist ranch at all -- it doesn't resonate with me personally. Not saying that it isn't there, but that I'm not the right person to make sense of it.
Whew, Mel, this is getting so complicated! Because now I see what you're saying as far as "church" symbolically representing "society." In other words, in this context church is devoid of specifically religious meaning except to establish the metaphor -- "fire and brimstone" simply means "disapproving of homosexuality," and so on. That makes perfect sense to me.
I slightly disagree with one small point: I have always interpreted "the fire-and-brimstone crowd" not as a criticism by Ennis of church/society -- i.e., Ennis moving toward accepting himself and realizing the fault lies with others -- but more of a statement that as a "sinner" he doesn't feel comfortable in that millieu because they'll judge/disapprove of/suspect him. That is, as far as he's concerned the fault could still be his.
I think I understand your idea, though, and I really like it.
But what I was talking about, and there may be something to this also, is a way of interpreting Ennis' experience more in terms of religion specifically. I'm not the perfect analyst of this, either, in that I didn't grow up in a church and am not a Christian, so my knowledge of Christianity comes only from what I've heard or read or studied along the way. But I don't think it's an accident that Mrs. Twist is so explicitly identified as a Christian, that there's a cross behind her as she's comforting Ennis and so on. Or that his experience at the ranch coincides with a sort of redemption, after which he's ready to change his ways (go to Alma's wedding). That model would also fit with the other references to church.
But the last image that the film leaves us with - the shirts still kept hidden in the closet - makes me less optimistic on that account. It's as if Ang Lee wants to stress that society's impact for men like Ennis hasn't changed much - it remains just as overwhelmingly limiting and crushing a force still at the end of those 20 years, - for Ennis, and for others like him.
True, the closet is a powerful symbol. And I agree there's not much indication at the end of the movie that
society has changed (unless you want to get back into the discussion of the tattooed woman!

)
But I do think there are lots of indications that
Ennis has changed -- that is, become more accepting of his sexuality. So when I said society has less influence on him than before, I meant that he is now more willing to ignore society's rules (represented here by the roundup) and instead act on behalf of love (attend the wedding). Unfortunately, the closet stands as a reminder that, in the case of Jack if not Alma, his transformation comes too late.