Theme: The theme, subject, or underlying thought of the poem is

1expressed in line 12 below:

2 

3"We Sinais climb and know it not;"

4 

5or more comprehensively in the group of four lines of which this is

6the conclusion. The organist's fingers wander listlessly over the keys

7at first; then come forms and figures from out of dreamland over the

8bridge of his careless melody, and gradually the vision takes

9consistent and expressive shape. So the poet comes upon his central

10subject, or theme, shaped from his wandering thought and imagination.