It is always important to consider quotes that are taken from a text in the context of the text as a whole, and this quote is no exception. This quote actually comes from Section 3 of his incredible poem, and comes just after a night he has spent with his lover. As he watches his lover walking away from him to get a towel, Whitman writes the following lines:
Shall I postpone my acceptation and realization and scream at my eyes,
That they turn from gazing after and down the road,
And forthwith cipher and show me to a cent,
Exactly the contents of one, and exactly the contents of two, and which is ahead?
These lines appear to suggest that Whitman does not want his eyes to try and perceive the future and what is going to happen but rather he wants his eyes to focus on himself and trying to work out who he is. The future is suggested through the picture of the eyes "gazing after and down the road," trying to work out what will happen next. However, Whitman would rather this his eyes "cipher and show me to a cent." Cipher in this context is a verb that means to decode or work out, and thus this quote concerns itself with the quest for self-knowledge. Whitman argues that it is better for humans to devote themselves to learning more about themselves and who they really are than to focus their energies on the somewhat futile task of trying to predict the future.