The metaphors that Dr. King uses in his speech to describe the condition of African- Americans at the time of the March on Washington have multiple layers. One such dimension was the fact that Dr. King wants to clearly state that "the dream" of which he speaks is part of the vision that the Framers had for American identity. Dr. King seeks to make Civil Rights part of the larger narrative of what it means to be in America. The use of terms like "manacles" and "chains" are effective images to describe how African- Americans are being denied their rightful part of American identity. The metal bands that are a part of the "manacles" metaphor and the bondage invoked with the "chains" metaphor helps to convey this sense of denial intrinsic to the African- American predicament. Dr. King's metaphors help to bring the idea of oppression to effectively communicate how the current inequalities that African- Americans faced as part of their daily being fundamentally deny the notion of the dream that the framers envisioned.
Another reason why Dr. King directly uses terms such as "manacles" and "chains" is meant to awaken the conscience of White Americans. Dr. King's tactical move was to broaden the Civil Rights struggle into a human struggle that all Americans could understand. Dr. King felt that the only way a broad based consensus regarding Civil Rights could be reached would be if White Americans could be employed in the struggle. To that end, Dr. King is able to use imagery to bring out the daily life for African- Americans. "Manacles of segregation" and "chains of discrimination" help to evoke the images of bondage, limitation, and oppression. Dr. King is deliberate in being able to use such imagery, as he wishes for White Americans to fully understand what life under segregation amounts to for people of color. In employing such metaphors, Dr. King is able to capture the imagination of the White American who might not have viewed Civil Rights in such a broad context.