What is the purpose of describing Frederick Douglass as "a man" in the first paragraph?

Federick Douglass was an escaped slave who became a prominent activist, author and public speaker. He became a leader in the abolitionist movement, which sought to end the practice of slavery, before and during the Civil War. Douglass wrote his autobiography to persuade readers that slavery should be abolished. To achieve his purpose, he describes the physical realities that slaves endure and his responses to his life as a slave.