What are the motifs in The Last Supper: A Novel by Charles McCarry?

Vengeance runs through Charles McCarry's novel The Last Supper, but its extent is revealed only in the final chapters. Barnabas "Barney" Wolkowicz is portrayed from the start as an underdog. He is physically ugly, held to the rank of a non-commissioned officer, and treated as a houseboy by his Yale-educated captain, Wadsworth "Waddy" Jessup. Twice Waddy proves himself a battlefield coward, leaving Barney behind for dead. The second time Barney is taken prisoner and has his teeth gouged out by bayonet to learn information that he does not know.