Lucid; that's my keyword for this film. There are other very good reviews posted here by other IMDB reviewers, and I've pleasurably devoured several of them (particularly concerning the movie's end, with Hawke's actual drinking of the drano and accompanying hallucination of Seyfried's character; which I only faintly noted as unusual when I watched it, and didn't truly latch on that the scene was not to be read straight-ly - Bravo, in interpretation, thank you IMDB reviewers!). So, to find something I want to contribute: the film and its translucent, white and boxed presentation, adds to this very lucid quality. Lucid for Ethan Hawke's character and how he is, and presenting the film as such.
Chris Nolan used light-whiteness in Insomnia, and First Reformed does so similarly, I feel. Both films interestingly involve searches for Truth; which may be coincidental but might also be conflated, without that connotation, as a state of lucidity? I find lucidity here, anyway. And the boxedness of non-widescreen presentation also talks to me about constraint, which again is a quality to the lucid state the Reverend is dealing with.
The themes of struggle and a Christian framework of understanding situated in this time and place, are compelling. I will always be suckered in by such discussions, I think, and this is definitely in my oeuvre. I most enjoyed the discussion with the manager of the Church's affairs that strove to point out the Reverend should not feel and indulge in Christ's suffering as much as he does. And I savoured seeing the Reverend's sexuality emerging now and again, through - what I regard not as Priestly, but middle-class and cultivated, repression. Repression and feelings of sexuality, and what to do with them, that we all have (see Freud, Foucault, Shakespeare, etc.).
The film starts with the Reverend's ambitious recording of his thoughts, and ends, apparently, in induced hallucination which the narrative plays straight. Lucidity in form, and, accordingly, compelling matter, here.