The poem sets a small, almost comic scene beside a large idea. A speaker looks at a single pear that has to serve as supper, and says it is "sorry" in the way a world without art would be sorry: bleak, thin, lacking something. The sentence runs in one breath, so the comparison lands before we have time to question it.
The title adds a joke. "Pear-shaped" is a phrase people use when things go wrong, and here it seems to hint at a meal, and perhaps a situation, that has not turned out well. Yet the pear is called "pretty," and that word complicates the gloom. The speaker seems to find some beauty in what little there is.
The mood is wry and rueful rather than truly despairing. There is humor in comparing a piece of fruit to a world without art, but also a quiet suggestion that beauty and nourishment are both needed, and that one pear can only offer so much of either.