Sean Scully has only visited Iona once, but his painting of the same name is "powerful and resonant"

Reading from left to right, as is our western way, the triptych begins with a wall of sombre colour, its surface obdurately dense: glossy, almost reflective; the rhythms of the blocks and bars irregular and defiantly painted in sweeping horizontal and broad-brushed vertical strokes. The light has gone from this painting, or perhaps not yet risen.

The first painting's restricted palette is continued in the third part of the triptych. However, here the bars of black and blue and grey are organised in ordered pairs, setting up a balance of gentle rhythms over layers of red and orange. Traces of high-toned light bleed through the gaps, suggesting a distinct shift in mood; the possibility, perhaps, of a way in, and a hint of hope or even harmony.

In between these low-key poles the central canvas presents a different story: this is the island between two panels of sea and sky and stone; a painting about life, created principally in reds and browns with hints of earthy greens and softer greys and pinks, all laid down over hot red, and in places a pale blue, glinting through the surface. Anchoring the painting, as with the panels on either side, are blocks of luxuriant black, wetter, heavier and yet simultaneously more fluid than the surrounding colours.

The triptych, Scully has said, is principally a narrative structure, and even at this distance from figuration there is a narrative of sorts implied by the relationship of one panel to the next. It is also a historically loaded form: the essential of the altarpiece, and outside the confines of religious art it suggests a grandeur of ambition as well as scale, the suggestion being that three panels have something to communicate that one alone could not.

In a lecture given at the Phillips Collection, Washington DC, in 2005, when he was midway through the painting of Iona, Scully described the continuity of art history: "I take my references from various points in art history – like Masaccio, who is very important to me, and Cimabue too. These are the artists I refer to in terms of colour, they use this dead light, a falling light. In Italian Quattrocento painting there is a beautiful sense of restrained exuberance – a lamentable exuberance would perhaps be a way to say it, or an exuberance of regret."

Scully could have been describing his Iona painting, and, strangely, he might also have been describing something of the small island in the Inner Hebrides that gave the painting its name.

The titling of abstract art has always invited debate: on one side stands the school of "Untitled"; a refusal to imply narrative and a willful denial of "meaning". On the other are the more poetic instincts of an artist like Scully, who embraces the layer of metaphoric potential that a title can bring to bear, though the painting always comes first. Scully didn't, in this instance, set out to make a triptych called Iona, but having made a painting that seemed to suggest something of the sea and stone that he recalled from a visit to the Hebrides 15 years earlier, he settled on the island's name as a suitable title.

Scully hasn't, I don't think, spent enough time in the Hebrides to know just how resonant a choice this was, but it's typical of his poetic intuition to have settled on a name that conjures many of the paradoxes that make Iona such a complex and resonant painting. So much of the character of this extraordinary work is analogous with island life: with an unlikely balance of hugeness and intimacy; with the phenomenon of seemingly infinite space, yet palpably held in one place.

The painting comes out at the viewer in a full frontal assault of surface, yet simultaneously offers a way in. And there's a rhythm that rolls from one panel to the next, a visual progression of the blocks of black, but at a pace so languid that time seems almost to stop. Hebridean life is lived at a similar pace and under a series of paradoxes that equally serve to describe Scully's painting: space and containment; softness and brutality; restraint and exuberance.

Iona, of all the Scottish islands, is a place with a rich and significant history. The abbey that George MacLeod re-built between the First and Second World War was founded in the 13th century, but the island's importance dates back to the sixth century and the monastic community founded by an expatriate Irishman, Colum Cille, St Columba, in 563AD. Under Columba this tiny island off Scotland's Western edge became one of the great centres of European thought and learning. From its position at the extreme fringe of the known world it found its place at the very centre of civilisation.

Scully, who is another expatriate Irishman, has made only one visit there, and that was in 1990, as part of a Hebridean tour. The experience though has stayed with him, prompted perhaps by a series of remarkable photographs, taken principally on the outer isles of Lewis and Harris.

It is remarkable how like Scully's paintings the world looks when viewed through the lens of his camera, but, as he has said, it is the sentiment that he holds onto rather than the subject: "The fundamental difference though between my working methods and those of the painters of the 19th century who made travel sketches is that I don't use images of what I've photographed, only the emotions."

And these emotions are still remarkably vivid, refreshed perhaps by more recent visits to the Aran islands on the West of Ireland, equally on the periphery of Europe. He has described the experience of standing at the edge of the sea: "Standing on the Old World looking out at the New World, as many people have done before… I try to paint this, this sense of the elemental coming together of land and sea, sky and land, of blocks coming together, side by side and stacked in horizon lines endlessly beginning and ending – the way the blocks of the world hug each other and brush up against each other, their weight, their air, their colour, and the soft uncertain space between them. I'm putting these into paintings."

Sean Scully's Iona is at the Ingleby Gallery, Edinburgh, 17 April until 26 June. This is an extract from Sean Scully: Iona, a 72-page book with essays by Sean Scully and Richard Ingleby, published to accompany the show. www.inglebygallery.com