If we--and now I mean the relatively conscious whites and the relatively conscious blacks, who must, like lovers, insist on, or create, the consciousness of the others--do not falter in our duty now, we may be able, handful that we are, to end the racial nightmare, and achieve our country, and change the history of the world.        
The Fire Next Time, 1963

If we …do not falter in our duty …, we may be able… to end the racial nightmare.

He then gracefully inserts elements and constructs sequences of elements to extend the depth and clarity of the thought.  Some of that complexity can be suggested by breaking the sentence into units variously indented on the page:

If we
--and now I mean
                   the relatively conscious whites
                   and the relatively conscious blacks,
                           who must,
                                like lovers,
                           insist on,
                           or create,
                           the consciousness of the others--
     do not falter in our duty now,
we
     may be able,
            handful that we are,
     to end the racial nightmare,
     and achieve our country,
     and change the history of the world.