For one thing, continued relevance through time. I can't imagine the novels of Philip Roth, or even Saul Bellow surviving much beyond our present age, though I've been wrong in a great many things and perhaps do not have the breadth of vision required to see them lasting. (I think of John Gould Cozzens, and other such writers so lauded during their own times--but then Bellow already has his academic cultus who may see to his literary survival.)
But on great books, to wit:
from The Inferno
Dante (tr. John Ciardi)As one who unwills what he wills, will stay
strong purposes with feeble second thoughts
until he spells all his first zeal away--so I hung back and balked on that dim coast
till thinking had worn out my enterprise,
so stout at starting and so early lost.
A moment, a lingering second in the second canto of The Divine Comedy, but a telling one. I know I can sympathize with one who starts out with vigorous purpose and think himself into absolute stasis if not retrograde motion. And he captures it perfectly. I often pelt myself with all that could go wrong, with all that is imperfect in my suggested enterprise, with all that is folly about it, and with the limited expectations I have put together for it.
Sheer foolishness--but human foolishness, and a foolishness with which the reader can readily empathize.
Of course, it isn't universality of situation that keeps a book in the canon of great books--also required are depth of insight, range of vision, and to some extent ultimate intent.
However you may judge is, Dante's Divine Comedy has these things and many, many more. If for some reason you have missed the opportunity to read it, take the time now--get a good edition with good notes to help you through the more difficult references--you'll be glad you did so. Perhaps then, you can say with Virgil:
"so welcome is your command that to my sense,
were it already fulfilled, it would yet seem tardy."
