Because Black Like Me is an autobiographical memoir rather than a novel, its themes stem from Griffin's real experiences and explicit opinions rather than from artistic creativity. As a result, Black Like Me is a fairly simple book; most of the important themes in the novel are discussed at length by Griffin during his long, contemplative diary entries. The most fundamental theme of Black Like Me, of course, is the question of identity and specifically the question of identity as it relates to race. Griffin's quest for social justice in America causes him (temporarily) to cast off his white identity and transform himself into a black man.
Griffin ostensibly wants to experience firsthand the obstacles and hardships of being black in America so that he may understand what life is like for blacks. As the book progresses, however, the profound change Griffin undergoes causes him to learn at least as much about himself. When he first looks into a mirror and sees a black man, Griffin feels a sensation of panic, a sense that he has lost his identity and no longer recognizes himself. After a few weeks of enduring the constant oppression, poverty, and difficulty of black society during segregation, Griffin has a new identity as a black man: now when he looks in the mirror, he sees a black man with a defeated hangdog look, a man who knows that his days will be difficult and his opportunities few.
Of course, the extraordinary personal change that Griffin undergoes as a black man is a powerful testament to the crucial importance of race as a factor of identity in a racist society, where one's position in the world is largely predetermined by the color of one's skin. Black Like Me is a short book, but the social message of Griffin's experience comes across through the book's narrative structure, which largely functions as a catalog of the different forms of racial oppression in the United States.
Griffin writes about the difficulties of finding food and shelter as a black man; the humiliation of not being able to find a restroom that blacks are allowed to use; the difficulties of performing basic actions like riding a bus, cashing a check, and sitting on a park bench without being interfered with by whites; the dehumanizing white obsession with black sexuality; the stench, filth, and ugliness of life in the ghetto; and the constant threat of physical violence at the hands of racist whites. An important theme of the novel is that blacks and whites behave so differently in one another's company that neither race has any real understanding of the other. As a white man, Griffin receives respect and courtesy from other whites, and suspicion and fear from blacks; as a black man, he receives hatred and hostility from most whites, and warmth and generosity from blacks.
This extraordinary generosity and sense of black solidarity is one of the only positive elements of Griffin's experience as a black man, which frequently leaves him depressed, confused, and full of self-hatred. Nevertheless, another important theme of the story is that even in an environment defined by the evils of racism, good people can and do exist and flourish. Whites like P.D. East and the construction worker from Alabama, and blacks like Sterling Williams and the mill worker, all offer proof that even though racism can warp the human spirit, it cannot destroy the human capacity for love and kindness. In the end, Griffin explicitly argues that love and tolerance are the only catalysts capable of changing society for the better—he is especially opposed to violence and the reactionary black supremacist movement typified by Malcolm X, which he considers another form of racism, likely to end in more violence and more misunderstanding.