Casgliad o Ysgrifau, by TH Parry-Williams, is the book of its author's lifetime. It brings together nearly all of the short essays that he published between 1928 and 1966, and in which he regularly cast back to his early childhood in Snowdonia. In my opinion, ysgrifau is better translated with the more literal "writings". For, more than anything else, Parry-Williams used the form to write out what Konstantin Mochulsky, referring to Dostoevsky, called the "enigma of his personality".

These reflections – on physics, metaphysics and everything in between – are matter enough for a lifetime. And for life. They are rooted in experience – something read or reflected upon or perceived more obliquely – but onto the pragmatic plane the author brings to bear his intellect and immense sensitivity. And an incomparable sense of language. The impression that he is writing for his own understanding – not to achieve some writerly goal – emanates from every page. Each individual piece is a rendering of deep, complicated existence.

TH Parry-Williams writes from a place of his own too: Rhyd-ddu, the small village in Snowdon's shadow which he left, more or less for good, aged 11. It is the equivalent in 20th-century Welsh-language literature of Proust's madeleine and the spur for meditations on the various shades of belonging. You come away from the Ysgrifau thinking that time spent "thinking about things", about the oddness of it all, isn't just not stupid, or a waste of time, but a fundamental requirement for a well-lived life.

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I return to these writings regularly – not least now, with the latest census data showing a worrying decline in the number of Welsh-speakers. The regret I feel a Parry-Williams's work not being available to a wider audience – in an English translation, for example, and subsequent inclusion, perhaps, on some Penguin Classics-type list – turns into a veritable sadness, however, at the prospect of it not even being available, in a meaningful way, to its primary audience for all that much longer either. There is often a significant discrepancy between the ability to speak a smaller language and the ability to read or write it.

The "Britain question" will be pulled every which way in the next 18 months. For my part, I can't help thinking that the "One Nation" that is "Stronger Together" ought, at the very least, to have been as interested in Parry-Williams's Rhyd-ddu as it ever was in Hardy's Wessex or in Dickens's London.

Owen Martell's novel 'Intermission' is published by Heinemann