Most words *mean* without one thinking of them *as* words. If I use the word "hammer" in a piece of writing, you tend to conjure the thing the word denotes, rather than the word - h a m m e r - itself. That's fine, of course, since it's the way we engage meaning effectively without constantly tripping over the self-consciousness that is required of thinking of words and words - the linguistic surface which is *not* itself the things it means.
Modern poets - and particularly postmodern poets, as we'll see - think almost wholly, or anyway quite often, about words as words. Williams was the great enthusiastic supporter of this idea. He once said (I'm paraphrasing): Poems aren't beautiful things or beautiful ideas. They're *words*! Not things but words! They're painted on the canvas - here! there! here! and there!
So think about a painting in which the meaning is not representational. The painting is not depictive of things. If that's so - or if that's mostly so - you have no choice but to look at the very medium used to make the painting. You look at the brushstrokes (the surface of the meaning-making) and not at the thing the brushstrokes normally denote.
Stein makes us look at the brushstrokes of language.