What is the central theme of "The Death of the Hired Man"?

The central theme of the poem is really a question. Which is more important, justice or mercy? The poem is a dialogue between a couple who own a farm and have periodically hired an undependable farmhand named Silas. Silas returns to their farm after begin gone for some time, and tells them that he wants to work for them again. Mary, who has talked to Silas thinks he has really come back order to have a place to die. Warren, on the other hand, believes that Silas has shown himself to be so undependable that they really own him nothing. Mary is seen as representing mercy and Warren represents Justice. In a long conversation, both Warren and Mary argue about what they should do about Silas. Warren believes that he owes Silas nothing because he has done nothing to deserve it. Mary believes that it doesn't matter what Silas has done in the past, he at least deserves to be taken care of because he cannot take care of himself. She tells her husband, "Be kind." Warren argues that he has been kind but " off he goes always when I need him the most." The discussion continues until Warren finally gives in a little. Ironically, just as Warren has accepted caring for Silas, he discovers the man has already died.