The Waldzell chapter of Glasperlenspiel contrasts Castalia (i.e the academia), in the person of Joseph Knecht, with the outside ("real") world, in the person of his friend Plinio.
In doing so it addresses a problem which often occupies the academics -- namely, the notion that their life, insulated as it is from the problems of the real world, is, by virtue of its irrelevance to the world, also somehow irrelevant per se.
This seems to be the major theme of GPS.
(It's worth noting, I suppose, that the real world does not really have a problem with academia's irrelevance and is happy to let it exist, irrelevant or not; the problem lies really in academia's mind. It is academics who are sometimes unhappy to be left alone to their doings; and who want these doings to be not just fun but also important; and it is they who imagine that the chief obstacle to its importance lies in its irrelevance).
The standard defense of academia against this (suicidal) attack proposes that academia is in fact useful to the outside world because basic research is needed to lay foundations for specific solutions to specific problems, educating large bodies of men is bound to produce at least some who are socially useful, etc.
Laudably, Hesse does not attempt this defense: such defense is self-defeating because it starts out by conceding that the life of the mind is only useful to the extent that it serves practical applications. It thereby automatically sets the life of the mind in a subservient position.
Hesse's intuition is like mine: that sooner or later all of humanity's immediate problems -- health, poverty, injustice, prejudice -- will be solved. And when they are solved, well, what then shall we do? We could decide to play computer games, of course; spit and catch; make love till we drop; or we could decide to dedicate ourselves to the pursuit if high-brow culture. A person who does so today is not really wasting his time, therefore: he is showing the way.
Now, I have solved all of my problems -- health, poverty, injustice have no more hold on me; I am therefore like that happy man of the future whose problems will all have been solved by the social activists of today. What I do with my time -- cultivate my mind -- is what that happy man of the future might choose to do with his: I read books, watch opera, visit museums, digest what I consume, think. To me this seems a life worth living.
But my life is not merely my life: considered and described, it represents a kind of roadmap for others. Just the sort of roadmap I so much wish others had left me.