By the time August Wilson's play Gem of the Ocean opens, slavery has been done for several decades. It is now 1904, but the play's characters have all been affected by slavery, and many of them are still not entirely free.
Aunt Esther still has the bill of sale that once showed her to be a slave. Of all the characters, she is probably the most free (along with Solly Two Kings), for she has accepted that true freedom comes with the acceptance of who one is and what one has done and the repentance of the evil one has carried out. She helps others find that freedom through the washing of their souls.
Solly Two Kings is also quite free even though he, too, was once a slave. He even carries a piece of the chain that once bound his ankle as a remembrance of the struggles he had. After escaping from slavery, Solly became a conductor on the Underground Railroad and brought sixty-two other slaves to freedom. He knows the true meaning of slavery and freedom, and that is why he sets the mill on fire. He realizes that the people who work in the mill are no better than slaves.
Citizen Barlow literally has to escape from Alabama, for Black people are not allowed to travel out of the state. The roads are closed, and he has to sneak out. Citizen is bound by both the guilt of having killed and man and the guilt of having stolen a bucket of nails that led to another man's death. Only through the spiritual journey led by Aunt Esther does he find freedom.
Caesar Wilks is just as bound as Citizen, but for different reasons. He thinks he has to enforce the law with rigidity and violence, and it turns him into a monster. He thinks that Black people would be better off in slavery because they are ruining themselves by misusing their freedom, but he doesn't understand that he himself is the one doing that.
We can see, then, that the deep meaning of Gem of the Ocean lies in the true significance and discovery of freedom.