What does Siddhartha experience while he meditates in Siddharta?
As Siddhartha meditates on the river at the direction of Vasudeva he listens to the river and what it has to say to him. Having already heard only the laugh of the river, Vasudeva encourages him to listen harder. When he hears the final word "Om--perfection" in the river, Siddharta experiences the healing that he has been desiring for so long. Note how his transformation is described as he comes to mirror the same serenity as Vasudeva possesses:
His smile was radiant as he looked at his friend, and now the same smile appeared on Siddharta's face. His wound was healing, his pain was dispersing; his Self had merged into unity.
Through the act of meditating therefore, Siddhartha experiences the feeling of forgetting his self and allowing himself to merge into the unity that he hears expressed in the single word "Om" that he hears in the river. This gives Siddhartha "the serenity of knowledge" as he is able to surrender himself to life and is living in harmony with what happens to him.