This is thy hour O Soul, thy free flight into the wordless,
Away from books, away from art, the day erased, the lesson done,
Thee fully forth emerging, silent, gazing, pondering the themes thou lovest best,
Night, sleep, death and the stars.
Yale criticism don Harold Bloom has argued that the “themes” Whitman mentions here—along with the theme of the sea—are closely associated with his mom, Louisa Van Velsor Whitman. Compare this passage from Walt’s “When Lilacs Last in the Dooryard Bloom’d”: 
 …But praise! praise! praise! 
 For the sure-enwinding arms of cool-enfolding Death. 
 Dark Mother, always gliding near, with soft feet, 
 Have none chanted for thee a chant of fullest welcome? 
 Then I chant it for thee—I glorify thee above all; I bring thee a song that when thou must indeed come, come unfalteringly. 
 Approach, strong Deliveress! When it is so—when thou hast taken them, I joyously sing the dead, Lost in the loving, floating ocean of thee, Laved in the flood of thy bliss, O Death. 
 From me to thee glad serenades, Dances for thee I propose, saluting thee—adornments and feastings for thee; And the sights of the open landscape, and the high-spread sky, are fitting, And life and the fields, and the huge and thoughtful night. 
 Bloom reads the “deliveress” here—Death—as a maternal figure, and the night/ocean imagery as an “Oedipal trespass”  or return to the womb. You may not agree with him, but once you’ve heard the theory, you can never quite get it out of your head as you read Whitman.
A Clear Midnight