I just stumbled across an entry I wrote in another section of this blog back in 2004. It was written in response to a friend's comment that she found Merton's writing (as summarized in The Intimate Merton) quite self-absorbed.
In order to respond, I went back through some of his writing. It seems that in both his public writings and in his journals, Merton is actually quite reticent about his innermost life. My own reaction to the later volumes of the journal when I first read them years ago, was to wonder where all his youthful fervor had gone, and where his "spirituality" was. The fact is, he keeps that substantially to himself - even while appearing to speak of his deepest experiences and feelings. He was, after all, writing to be read by others, even though he speaks of wanting a place to write where he can say everything. There is only one place I know of where the screen falls for a moment - and it is not in his journals but in his correspondence.
Michael Mott in The Seven Mountains of Thomas Merton quotes from a letter Merton wrote in 1966 to a Sufi mystic with whom he had corresponded for a number of years, and who had evidently asked what his daily life and meditation were like. It is worth quoting in full:
At sunrise I say another office of psalms, etc., then begin my manual work, which includes sweeping, cleaning, cutting wood, and other necessary jobs. This finishes about nine o'clock, at which time I say another office of psalms. If I have time I may write a few letters, usually short (today is Sunday and I have more time). After this I go down to the monastery to say Mass, as I am not yet permitted to offer Mass in the hermitage. Saying Mass requires an altar, an acolyte who serves the Mass, special vestments, candles, and so on. It is in a way better to have all this at the monastery. It would be hard to care for so many things and keep them clean at the hermitage. After Mass I take one cooked meal in the monastery. Then I return immediately to the hermitage, usually without seeing or speaking to anyone except the ones I happen to meet as I go from place to place (these I do not ordinarily speak to as we have a rule of strict silence.) (When I speak it is to the Abbot, whom I see once a week, or to someone in a position of authority, about necessary business.)
On returning to the hermitage I do some light reading, and then say another office, about one o'clock. This is followed by another hour or more of meditation. On feast days I can take an hour and a half or two hours for this afternoon meditation. Then I work at my writing. Usually I do not have more than an hour and a half or two hours at most for this each day. Following that, it being now late afternoon (about four) I say another office of psalms, and prepare for myself a light supper. I keep down to a minimum of cooking, usually only tea or soup, and make a sandwich of some sort. Thus I have only a minimum of dishes to wash. After supper I have another hour or more of meditation, after which I go to bed.
This in itself is evidence of a deep interior life - but the next part makes it explicit.
Mott notes at this point that Merton "had always felt it was wrong to discuss his own religious practices in any detail … He had been reserved on this subject even in his private writing." However, in writing to this friend he made an exception. Merton went on:
I do not ordinarily write about such things and ask you therefore to be discreet about it. But I write this as a testimony of confidence and friendship. [Seven Mountains, pp. 432-433]

