Sean Scully's brush is five inches wide, heavy with wet oil paint. He built the pictures in "Sean Scully: Wall of Light" at the Phillips Collection of slabs of layered color, one color on another, as one might build with boulders, so that being in his show is like standing in a room whose walls are stacked-together stones. Colored light seeps through them and shines through the chinks. It's like being in a castle keep. The air feels heavy with the weight of the stone and with that of the olden days. The mood is valiant and assertive and pledged.

Duncan Phillips (1886-1966) shared that faith. When he opened his museum in the District just after World War I, he already sensed the coming of a wholly abstract art and felt its importance. After World War II, he took us all the way to Rothko. Once upon a time -- but not anymore -- many advanced artists shared the Phillips's vision. Their grail was "pure abstraction." Most of them are gone now. In 2005, if you had to pick a painter to bear the banner forward, Scully would be the one.

He was born in Ireland in 1945. A longtime Londoner and a longtime New Yorker, he also is a thoroughly credentialed, widely traveled, international art star. Scully has had museum shows in London, Boston, Madrid, Finland and Australia. He's had teaching gigs at Princeton and Oxford. His new pictures carry prices in the neighborhood of $500,000.

Art, you may have noticed, has gone electric. The green beads of on-lights, the hum of computers and the flicker of videos now fill the with-it galleries. In the context of such newness, Scully strikes the viewer as a figure from a bygone age, a solitary seeker, muscular and tested, a true knight of the stripe.

He tends to shape his stripes, to shorten and thicken them until they feel like ingots. The pictures he makes from them aren't in the least ironic. Nor are they wan or witty. They are much too thickly painted to look like supergraphics. He has something else in mind.

He once said that he sought to paint "severe, invulnerable canvases so I could be in this environment and not be exposed. I spent years making my paintings fortresslike." We imagine knights as muscular, armored and committed, and, of course, used to fortresses. One feels this in the heft of Scully's strange and poignant art.

What makes it strange is that there is a mystery in stripes.

Try this: Draw an outline of a box, then divide it into two with one horizontal line. You've made a sort of seascape -- the sky above, the sea below, between them the horizon. Now turn your drawing on its side so that the line is vertical. Where once you sensed extended space, now you feel the presence of two figures, or columns, standing side by side. Scully ceaselessly exploits this switch. Suggestions of deep distance, and then of standing presences, keep replacing one another in the square cells of his art.

What makes his painting poignant is that his quest may well be fruitless. By now we've come to see, and Scully surely knows this, that there's really no such thing as purely abstract art.

All paintings are pictures of something; so are Scully's. The painter says his "Wall of Light Rain" (2003) takes its title from Bob Dylan's "A Hard Rain's a-Gonna Fall," but the viewer need not reach that far. Plain old Irish rain also is depicted. If you stare at it awhile, the gray divided square at the focus of the image will open all of a sudden like a wall-dissolving window looking far out to the ocean through North Atlantic mist. There is sun warmth in these paintings, too, as well as intimations of standing stones, doorways, the meadows of Bavaria and the glare of Barcelona, as well as that seething mix of rust, steam and shadow that is so characteristic of the canyons of New York.

Scully's work is often beautiful. The beauty that he shows us is not something he's invented. He's also found it in the world. To make this point explicit the Phillips has included photographs by Scully in this painting exhibition. One of these depicts the gale-resisting stone wall of a West-of-Ireland Aran Islands shack. The muted, old and awkward beauty of wall is very much the beauty of Scully's pieced-together art.

Here is something else that his oil paintings are pictures of. They cite a clear tradition of geometrical abstraction, and they wear it like a badge. Looking at these Scullys, some old and some new, you cannot help recalling painters who preceded him, Kasimir Malevich first, he of the "Black Square," and Piet Mondrian, Hans Hoffmann and Giorgio Morandi, too, Richard Serra, Frank Stella and many more. Especially Mark Rothko. The Phillips, as a whole, pays homage to their enterprise. The many photo-footnotes of other artists' paintings that are sprinkled as reminders through Stephen Bennett Phillips's exhibition catalogue make Scully's debts apparent. If you like the things they painted, Sean Scully is your champion. He does honor to that fellowship. Perhaps that is one reason his pictures feel inhabited. The painters of that company seem to stand around like ghosts in the dense light of his show.

Sean Scully: Wall of Light includes 39 oils from the "Wall of Light" series, which the painter began in 1998, as well as 44 additional pictures from earlier decades. Three of these are photographs. A grant from UBS supported the exhibit. The Phillips Collection, 1600 21st St. NW, is open Tuesday-Saturday, 10 a.m.-5 p.m. (Thursdays till 8:30). Admission to the show is $9 for adults, $7 for students and seniors. For information call 202-387-2151 or see www.phillipscollection.org. The exhibition will travel to Fort Worth, Cincinnati and the Metropolitan Museum of Art in New York after closing here Jan. 8.

Scully's "Bridge" acknowledges 20th-century abstract artists while also evoking its own emotions.The Sean Scully show at the Phillips Collection includes photographs by Scully as well as paintings. The 2000 oil "Wall of Light: Blue Blue," left, relates to a photograph of an Aran Islands stone wall, "Stone Shack End," 1994.