The human ecologist, Alastair McIntosh has already established his credentials as one of Scotland’s greatest living authors. Soil and Soul and Hell and High Water achieved that a few years ago and, since then, Island Spirituality and Spiritual Activism (co-authored with Matt Carmichael) have kept the pot boiling.

His latest offering, Poacher’s Pilgrimage, is a tour de force. If this was just a travel book, taking us on a journey up and around the hills and across and through the moorland and rivers of Harris and Lewis, it would be a wonderfully evocative story of a man revisiting his child-hood haunts and reminiscing about a past long gone, as he undertakes a twelve-day hike in one of Scotland’s more remote parts.

McIntosh’s writing is so crisp and tightly woven that it is both hard to skim – each word seems carefully chosen for its particular task – and hard to put down. You really want to know if he made it to a safe place to pitch his tent as the next storm rolled in – or if there really is a hidden well under that moss-covered boulder. He captures perfectly the wilderness with all its awe and charm.

But, this is more than just a travel book. With this writer, you always get more than you thought you’d bargained for. What learning, he reveals, in both depth and breadth as he takes us on a spiritual and mystical journey. Who else would be equally at ease (and equally accepted) discussing mutually assured destruction with the country’s leading generals, over drinks at their staff college, or recalling the stories of the sìth (the faerie tradition) and second sight with an elderly resident of the islands, living by paraffin lamp in her isolated cottage?

Who else would cite Patti Smith, Buffy St Marie, John Martyn, Barclay James Harvest and Pink Floyd alongside Yeats, Erich Fromm, JM Barrie, Thomas Merton, Martin Luther, Walter Wink, Freud and Disraeli, and numerous island and Gaelic scholars and clergymen? Indeed, McIntosh lays out his stall early: seeking “to penetrate in ways that question the very structures of space and time, exploring consciousness and meaning in the deeper realms of life within the soul.” It’s a quest to find out what “we’re inside of”, an ecology of the imagination.

McIntosh ponders whether recent breakthroughs in neuroscience open possibilities for new links between science and theology. Time, as a moving image of eternity. Could it be, he asks, “that everything that ever was, or waits to be, just is?” Is that what it means to “inhabit eternity”? The sìthean lore of the islands seems to recognise “a realm beyond the mundane constraints of time and space.” Or, as he later puts it, the realm of the true underlying nature of all things. Life as love made manifest.

Mythos and Logos, the imaginal and the rational, fact and fable. Grappling with dichotomies and paradoxes, contradictions and the holding in creative tension of two worldviews. “Caledonian antisyzygy” is the term he borrows to name the Scottish version: as Scots ponder our place in the UK and the EU, the reader is driven to ask: might that be our lot at this time?

I read this book in the immediate aftermath of the Brexit vote and the publication of the report of the Chilcot inquiry. Writing prior to these events, McIntosh’s reflections on a leader’s “political paranoia”, living out the myth of redemptive violence, seem prophetic. It seems that McIntosh, while immersed in the folk traditions and religious gravity of the Western Isles, simultaneously speaks to us about the most contemporary and pressing of issues. He doesn’t shirk from challenging religion’s association with, and co-option of, God (Dieu et mon Droit) in support of, violence, or Christianity’s continued absorption with legalism, so contrary he argues to the non-violent, loving message of Jesus, who spent his life suffering among the poor.

A theology of fear discredits any god of love, he writes. And yet, he speaks sympathetically of the military leaders he has known, so often more aware of the tragedy of war than their political masters. “We all take up positions on a long front. None of us can quite see how it looks from the next person’s post.”

He ruminates on the Calvinism of the Outer Hebrides, with its deeply rooted, binary instructional religiosity whose appearance coincided with the coming of outside landed power to occupy the land. What does it mean to be a connected human being he asks? To see the writing on the walls? To work from an inner place of integrity? To achieve metanoia, the radical transformation from deep within that is so much more than simplistic expressions of biblical repentance? And how to avoid the “unheimlich”, that estrangement between the internal and external worlds, with its potential to trace its steps between generations?

We are, he argues, today faced with a colonisation of the soul, just as so many parts of the Outer Hebrides were colonised by the forces of Empire in the clearing of the land of its ancient peoples to make way for sheep-rearing. And violence: does it come from the very cravings, the unresolved anxieties, which are at war within each of us? The failure to accept our Jungian “shadow’ side – with the consequences of that denial, as we project our shadows onto others and become slaves to the self-centredness that blinds us to deeper truths…..

The last section of the book presents more of a direct challenge to some fundamental religious thinking, not least to the pivotal Calvinist notion of penal substitutionary atonement, that Jesus was brutally murdered to relieve us of the consequences of divine wrath at our sin. That only works, McIntosh asserts, if the “carriage of Christianity is drawn by an Old Testament warhorse”. He prefers the idea of liberation, for-give-ness, the cross as the supreme symbol of nonviolence. The second coming? It always is, always was and always will be, Christ as cosmic enlightenment.

McIntosh is, as he notes in his travels, metaphorically and in reality re-opening old wells, a quest which attains real significance as the story unfolds. An old friend in Shawbost on Lewis observes, “we all know that something isn’t right….a change has come about that we hardly understood before it was too late.” This is a real call to greater consciousness, to an awareness that profound shifts are occurring.

And yet: “You won’t go forwards looking backwards!” Courage is the thing. Recalling JM Barrie’s Rectorial address at the University of St Andrews in 1922, McIntosh reminds us that, if we let things slide, if courage goes, “all goes”. There is real courage in this writing. It is a wide-ranging survey of deep things set in the narrow geographical corridor of the Outer Hebrides. That serves as a juxtaposition which is both endearing and personal while, at the same time, challenging and cosmic.

This is a book to savour, to ponder and to work with. McIntosh has given a lot of himself in writing it. He asks questions of himself and of us all. It merits immersion and much reflection.

John Sturrock QC is a mediator and founder and chief executive of Core Solutions Group

Poacher’s Pilgrimage by Alastair McIntosh. Pub by Birlinn. 352 pp. £20.