To gain further insight into van Gogh’s religious beliefs as they can be seen in the Nuenen Church Tower art, what better source to serve as interpreter than his own writings? The artist was a prolific writer, constantly sending letters to his brother, Theo, with whom he shared his most intimate struggles, frustrations, and dreams for his art. Here, then, are some sections from the letters Vincent wrote to his brother, from around the time of his period in Nuenen (some slightly before and after):
From Letter 164 (Etten, Holland, late December 1881):
“Whenever I tell Father anything, it goes in one ear and out the other, and that certainly applies no less to Mother, and similarly I find Father and Mother’s sermons and ideas about God, people, morality and virtue a lot of stuff and nonsense. I too read the Bible occasionally, just as I sometimes read Michelet or Balzac or Eliot, but I see quite different things in the Bible from what Father does, and what Father in his little academic way gleans from it I cannot find in it at all.”
“…and then J.P.S. went off to church. No wonder one grows hardened there and turns to stone, as I know from my own experience.
And so, as far as the person in question, your brother, is concerned, he refused to allow himself to be browbeaten.
But that didn’t alter the fact that he had a browbeaten feeling, as if he had been standing too long against a cold, hard whitewashed church wall.”
“I still felt chilled to the marrow, that is, to the marrow of my soul, by the above-mentioned imaginary or non-imaginary church wall. And I said to myself, you don’t want to let that fatal feeling browbeat you.”
“If there is anything I regret then it is that period when I allowed mystical and theological profundities to mislead me into withdrawing too much into myself. I have gradually come to change my mind.”
“she is in a kind of prison, she too is poor and cannot do as she pleases, she feels a kind of resignation, and it is my belief that the Jesuitisms of clergymen and devout ladies often make a greater impression on her than on me, Jesuitisms which, precisely because I have acquired some dessous de cartes [inside information], no longer have any hold on me now.”
“Incidentally, have you ever heard Mauve preach? I’ve heard him mimicking several clergymen – once he preached about Peter’s boat. The sermon was divided into 3 parts: 1st, was he given the boat or did he inherit it? 2nd, did he purchase it in installments or by taking out shares? 3rd, had he (dreadful thought) stolen it? Then he went on to preach about “the Lord’s good intentions” and about “the Tigris and the Euphrates” and finally he mimicked J.P.S. marrying A. [Anna Carbentus, Vincent’s cousin] and Lecomte.
But when I told him that I had once said during a discussion with Father that I believed that even in church, even in the pulpit, one could say something edifying, M. agreed. And then he mimicked Father Bernhard: “God – God – is almighty – He has made the sea, He has made the earth and the sky and the stars and the sun and the moon, He can do everything – everything – but – no, He is not almighty, there is one thing that He cannot do. What is the one thing that God Almighty cannot do? God Almighty cannot cast out a sinner.”
From Letter 344 (Nuenen, 5 December 1883):
“I thought of you, brother, during that long walk across the heath, in the evening, in the storm. I thought of a passage, I don’t know from what book: ‘Deux yeux éclaircies par de vraies larmes veillaient;’ [two eyes were awake, brightened by genuine tears]. I thought, I am disillusioned. I thought, I have believed in many things which I now know are really sorry fallacies – I thought, Those eyes of mine, here on this gloomy evening, wide awake in this deserted region – if they have been full of tears at times, why shouldn’t these have been wrung from me by a sorrow that disenchants – yes – and disturbs illusions – but at the same time – makes one wide awake.
I thought, It’s impossible that Theo is satisfied with many things that worry me?
Is it possible that it is only my own melancholy when I cannot enjoy things as I used to do?
In short, 
I thought, Is it possible that I take gold for tinsel? Do I call withered a thing that is in full bloom? I could not find an answer, can you? Are you sure that there isn’t a far-advanced, inexorable decadence everywhere? Give me courage, if you have courage yourself, but I ask you in my turn, ‘Do not flatter me.’”
From Letter 347 (Nuenen, 18 December 1883):
“Theo, in the past I often quarreled with Father, because Father said, dictatorially:
‘It is like this,’ and I told him, ‘Pa, you are contradicting yourself, what you say militates absolutely against what you vaguely feel at your heart’s core, even if you do not want to feel it.’ Theo, I stopped quarreling with Father wholly and completely long ago, because it is now clear to me that Father has never reflected upon certain very important things, and never will reflect upon them, and that he clings to a system and does not reason, nor did he ever, nor will he ever reason on the basis of the naked facts. There are too many who do as he does, so that he always finds certain support and strength in the thought, Everyone thinks this about it (namely primarily all the well-regulated, respectable clergymen). But he has no other strength, and it is all built on convention and a system, otherwise it would collapse like any other vanity. Father does not wrestle with the plain truth. But now I am of the opinion that one is one’s own enemy if one does not want to think things out, if one does not say (especially in one’s youth): Look here, for myself I do not want to be sustained by a system, I want to attack things according to reason and conscience. I take less notice of my own father, though he is not a bad man, and though I do not speak about him, than I do of people in whom I find more truth.”
“As far as religion is concerned, I find less of it in Father than in Uncle Jan, for instance, though it stands to reason that many would say the reverse. I think Father the opposite of a man of faith.”
“At the time [of working as an art dealer] I did violence to myself, and was moreover so oppressed by the preoccupation that I was no painter, that even after I had left G. & Co, I never thought of becoming one but turned to something else (which was a second mistake on top of the first) [the ministry], feeling discouraged about my prospects."
Letter 378 (Nuenen, October 1884):
"Oh, I am no friend of present-day Christianity, though its Founder was sublime – I have seen through present-day Christianity only too well. That icy coldness hypnotized even me, in my youth – but I have taken my revenge since then."
Letter 490 (Arles, 26 May 1888):
“I feel more and more that we must not judge of God from this world, it’s just a study that didn’t come off. What can you do with a study that has gone wrong? – if you are fond of the artist, you do not find much to criticize – you hold your tongue. But you have the right to ask for something better. We should have to see other works by the same hand though; this world was evidently slapped together in a hurry on one of his bad days, when the artist didn’t know what he was doing or didn’t have his wits about him. All the same, according to what the legend says, this good old God took a terrible lot of trouble over this world-study of his.
I am inclined to think that the legend is right, but then the study is ruined in so many ways. It is only a master who can make such a blunder, and perhaps that is the best consolation we can have out of it, since in that case we have a right to hope that we’ll see 
the same creative hand get even with itself. And this life of ours, so much criticized, and for good and even exalted reasons, we must not take it for anything but what it is, and go on hoping that in some other life we’ll see something better than this.”