Based on the poem, the essence of human identity is to move. Human definition is seen through the lens of action, of initiating interaction between the individual and their world. In a word, movement is what defines human identity:
One lacks direct instinct, because one wakes
Afloat on movement that divides and breaks.
One joins the movement in a valueless world,
Crossing it, till, both hurler and the hurled,
One moves as well, always toward, toward.
"Movement in a valueless world" and movement "always toward" help to define human identity as one of fluidity.
Transformation is brought about by movement such as with motorcycles and birds. The poem sees movement as something that humans have to do. The idea of "purpose" is best accomplished through movement:
At worse, one is in motion; and at best,
Reaching no absolute, in which to rest,
One is always nearer by not keeping still.
The closing line of the poem is one in which movement is reflected as part of what it means to be human. Human beings might have a choice to keep still and to move, but the condition of identity is one in which movement is essential. Movement is what defines individual consciousness, towards an end that might not be certain or even in lucid view. However, "one is always nearer by not keeping still."