The central theme of the poem is the understanding of the most important type of knowledge, that is, knowledge that cannot be communicated except through a shared sense of wonder. The “lesson complete” is the lesson felt, experienced, and endured; it is not a lesson learned in textbooks or in lectures. The most important kind of knowledge is gained through a relaxation of the soul, making possible the understanding of the wonderful nature of natural phenomena.
As the poem’s title suggests, the great poet functions as a great teacher. The poet as teacher is a common nineteenth century figure. The poet does not instruct so much as he shows the way through his own example. Readers of Leaves of Grass will recognize the theme of the difficulty of communicating the sense of wonder as pervasive in Whitman’s work. The short poem “When I Heard the Learn’d Astronomer,” to cite a familiar example, narrates two scenes: The first scene shows the poet attending an astronomy lecture, while the second scene relates the narrator’s departure from the lecture to stare “in perfect silence at the stars.” The lecture leaves the poet “tired and sick,” but he is refreshed when he looks up at the stars, having escaped “the charts and diagrams.” The relief from such depression consists in the sense of wonder awakened by simply staring up at the stars. True learning comes about as a result of the sense of wonder rather than formal education.
The theme of equality, of the essential nobility of all human beings whatever their occupation, educational level, economic status, or location is, again, one that all readers of Leaves of Grass have come to expect from the great poet of democracy. Another theme, the assertion of immortality and the sense of wonder associated with the belief in immortality is, to most critics and scholars who have commented on this poem, insufficiently developed. As one of the most important doctrines of Leaves of Grass, it is more satisfactorily treated in poems such as “Song of the Rolling Earth” and “Salut au Monde!”