I, too, read this book recently....You should finish it. I've also used Baldwin's "white too long" statement in a number of essays.
The bottom line of Baldwin's statement is that it is impossible to be born and raised -- socialized -- as a so-called "white" person in this country and throughout the entire "West" without being inflicted with the lifelong scourge of white racism/white supremacy. No matter how "liberal" or "left" or even "radical" one may think he or she is. In short, "whiteness" (the idea that "white" folks are somehow "superior" to everybody else) is now in the DNA of these people and cannot and will not be extracted or eliminated until they themselves -- as a "race" -- are eliminated or "disappeared."