The single theme of the novel is Siddhartha’s search for unity, which is identical with his search for the true nature of the self. He cannot find either by rejecting the world, but neither can he take the opposite route and indulge the senses. He must indeed embrace the world, but only when he is able to experience it sub specie aeternitatis, in its essential form. He must come to know that the individual self, the Atman, is identical to the universal self, the Brahman, although by the end of the novel the terms have shifted. He has, even while remaining an individual, become indistinguishable from the universal nature of the Buddha.
To attain this enlightenment, the most important lesson he learns is the ability to be passive, to wait and listen. If he can cease his own small willing and striving, he can learn to embrace the great contradictory harmonies of the world. He can, in his own person, reconcile all the strife of opposites; he can overcome the illusion of time and thus experience the myriad, diverse forms and events—past, present, and future—as a simultaneous present, and hold them in a quiet serenity which accepts and loves everything, seeing no fault.
Hesse’s great image, in which the whole meaning of the novel is contained, is the river. Siddhartha is reborn as he sleeps by the river’s edge, and he resolves to stay there and learn from it. Vasudeva has spent a lifetime ferrying travelers across the river (in Buddhist thought, enlightenment is said to be the knowledge which goes “to the other shore,” and the sage is the one who steers the boat). The river symbolizes life. It is from the river that Siddhartha learns that time has no existence. The river is everywhere at the same time; it flows on forever and has neither past nor future. Siddhartha realizes that this quality is also true of human life and that suffering takes place only within that false mental construct which is called time, yet which has no reality.
Siddhartha hears all the different voices of the river and discerns all the forms it contains. He sees his own past and all the people he has known. He also sees the insatiable desire which drives all life toward its goal. Yet he also knows that every act is necessary and good; every thing and every creature contains the Buddha-nature within it, and that all goals are reached, after which life changes its form and continues. When he hears the ten thousand voices of the river together at the same time, he realizes that none is separate from any of the others, and when he does not try to attach himself to any one particular voice, the sound of the river becomes a great song, the music of life in its eternal perfection. Armed with this knowledge, he can love and respect all creatures.