Answer:
For instance, the Master is described using some simple but effective metaphors. He's a "hard lump of clay" (6), detached and unaffected by the suffering inflicted every day on his behalf. What kind of monster "wouldn't be moved" (6) by all of this? Um, a monstrous one. To be honest, though, we'd say that the Master is able to remain so detached because the Overseer and Driver do the dirty work.
Later, the characterization of the non-flying slaves builds sympathy for their plight. Although they've just witnessed a miraculous occurrence that fulfills their wildest dreams, they "were too afraid to shout" (24). For them, there's still a difficult road ahead. This also gives us a sense of the psychological effects of slavery, revealing the painful internal turmoil that must've been felt on a daily basis.