James McBride wrote The Color of Water as an autobiographical reflection of his journey to discover his past, for he was always aware that what happened before him was a major factor in who he became. The piece of his past he had to discover was his mother's past, as he knew anything he wanted to know about the men she married. His mother, Ruth, on the other hand, adamantly (and successfully) kept her past hidden from her children.
James has always known his mother is obviously not a black woman, and her beliefs about religion, education, and family are in distinct conflict with the way she lives her life and raises her children. While his siblings do not appear to be as affected by these contradictions, James is, and this need to unveil his past consumes him. When Ruth finally gives him a kernel of information from which he can search, James begins to delve into his mother's (and therefore his own) past.
While he does discover the answers to most of his questions and finds that they do help him sort out his own life, his greatest discovery is that the past is a disappointing--and in some ways a non-existent--entity.
Sometimes without conscious realization, our thoughts, our faith, our interests are entered into the past. We talk about other times, other places, other persons, and lose our living hold on the present. Sometimes we think if we could just go back in time we would be happy. But anyone who attempts to reenter the past is sure to be disappointed. Anyone who has ever revisited the place of his birth after years of absence is shocked by the differences between the way the place actually is, and the way he has remembered it. He may walk along old familiar streets and roads, but he is a stranger in a strange land. He has thought of this place as home, but he finds he is no longer here even in spirit. He has gone onto a new and different life, and in thinking longingly of the past, he has been giving thought and interest to something that no longer really exists.
This quote displays McBride's understanding that living in the present is much more productive, and certainly more real, than dwelling on the things which are past. He is able to reconcile his mother's past with her actions, which helps him better understand his own place (culture, heritage, family, history) in the world. And then he is able to put these things where they belong--in the past.