This moment of the play is one rich with meaning, yet open to interpretation. When Gabriel appears onstage in the play, he discusses his relationship with Saint Peter and his future role opening the gates of heaven.
His life is filled with his singing and his expressed wait for St. Peter to call upon Gabriel to open the gates of heaven.
Practically speaking, Gabriel is mentally unstable. He cannot live alone or care for himself. Gabriel's speeches about his relationship to the angels is mere performance; not to be believed.
We might take this fact as a primary insight in investigating the meaning of Gabriel's dance and comment at the end of the play.
After all of Troy Maxson's challenges, after his strife and turmoil and failed relationships, the final comment on his life is one of mere gesture, though that gesture attempts to be truly meaningful, even profound.
Had Troy Maxson realized that he did not need to struggle so mightily but might have yielded at a number of points (with his wife and with his son), he may have found some solace for his bitterness and some relief from his unrelenting toil.
The idea that Troy's life could have been happier and easier if he would have simply chosen to relent in his hardness provides an intepretation that suggests Troy's life was itself a gesture, a failed attempt at doing something meaningful. He did not need to be so bitter, so hard, and so stubborn.
Alternatively, we can also see Gabriel's exclamation as an enactment of his character. His crazy dance is part of who he is and he is powerless to change this. There is no judgment implied in Gabriel's dance. As Troy's brother, Gabriel bears no grudge despite the Troy's exploitation of him. This love again is an unconditional part of his character.
Gabriel's consistency in the end can be taken as a commentary on Troy's unchanging nature. Just as Gabriel simply and frankly "is who he is", Troy remains unchanged by his circumstances, continuing to fight against his limitations, repeat his mistakes, and repeat the mistakes of his father.
Troy lives in the past and fails to recognize that the world has changed...Thus, he repeats the mistakes of the previous generation.
Seen in this way, Troy's actions and decisions in the play are consistent with his nature. Troy is as powerless to change his nature as his brother Gabriel. His attitudes as parent, professional, and as husband are continuous with those of his father, as is the basic pattern of his life.