Need some help on Walt Whitman's poem, For Him I Sing
"FOR him I sing,
(As some perennial tree, out of its roots, the present on the past:)
With time and space I him dilate—and fuse the immortal laws,
To make himself, by them, the law unto himself. "
I don't really get it. Is this poem talking about immortal love? The poet's keens of nature? Or any other things else?