Sean Scully was explaining all this at the South London Gallery where an exhibition of his new works is on show, his largest gathering of big paintings in a non-commercial gallery since the Whitechapel show in 1989. Now approaching his middle fifties, he is a big bruiser of a displaced Irishman - he has workshops in Deptford, New York and Barcelona - who hunches over to contemplate his twisting and turning hands as he speaks.
His appearance - those smooth, plum-coloured cheeks; that close-cropped white hair; that smallish mouth, strangely twisted askew - seems part convict, part cherub. He speaks with the reticent gentleness of an unclubby painter who is no longer being torn apart by the desire to be fashionable in the way that he was 15 years ago in New York - a painter who has no particular wish to be the Frank Stella of his day; in fact, no wish even to be regarded as a contemporary at all. Now Scully has settled down into a knowledge of his own strengths and limitations as an artist.
"I want my paintings to move people," says Scully, who sounds part Irish and part vestigially South London when he speaks. Though unusual, the persistent omission of the "t" from the word "painting" sounds genuinely significant - as if they were in the habit of crying out to us from the walls.
There are 11 new canvases in this show, and two of them contain the word "light" in the title. Wall of Light Yellow will be compositionally familiar to all Scully watchers. It consists of a characteristically flat, rhythmical wall of repeated horizontal and vertical bands. The colours are muted, harmonious, in tune with the hues of the natural world - more reminiscent of its slow, autumnal dying-away, however, than of its vital, spring-time burgeoning. There is no colour here that might not have been fashioned by the earth itself. "I like to make something that's like the world," he tells us, "out of the very stuff of it, so that it's common to all of us, enterable."
These panels of discrete colour have been painted and re-painted, often roughly, tempestuously, nervily, so that the whole moves towards tonal coherence within a kind of stockade of contained energy. The panels butt against each other quite roughly - like pairs of young, mettlesome bullocks locking their horns.
And then there is the paradox of the painting's title to consider too. Wall of light? It is seldom a characteristic of walls to admit light. The key to this title is a story Scully tells about his childhood. As a boy in Croydon, he would pass a Roman Catholic Church on his way to school. Stealing in one day, he found glorious hosannas of fat, burning candles, which seduced him to such an extent that he stole some and buried them in the garden.
When the priest came looking for the thief, Scully was reluctant to own up until he was told that God, who shows great mercy to sinners, would show yet more mercy to those who repented of their sins, even more than if they had not sinned in the first place. The young Scully, ever opportunistic, led him out to the garden.
"Candles," says Scully, "I love them. It is so about the beauty of the form, that ascending feeling. I also love them for their ability to be both a solid material and yet capable of embodying light - that is what I wish for my own paintings. The idea is to make a skin that is full of the possibility of light. Light means hope or illumination. The words light and spirit are interchangeable in my opinion..."
Light? Spirit? There is clearly a religious sensibility at work here. But then abstract art in our century - think of Kandinsky alone - has often been an expression of religious impulse.
But Scully goes further still. "When I converted from figuration - which is how I painted when I studied at Croydon in the 1960s - to abstraction, it was because I believed it was the fulfilment of the church's - and art's - destiny: the church to lose its position of influence, and art's to take it over..."
By this time the light is fading somewhat, and Sean Scully is swigging, quite rhythmically, from a generous tumbler of red wine.
`Sean Scully: New Paintings', South London Gallery, 65 Peckham Road, London SE5 (0171-703 6120) until 1 August