Why does Goliath explain how representative warfare is meant to work?
1 Samuel 17:8–9 (ESV)
8He stood and shouted to the ranks of Israel, “Why have you come out to draw up for battle? Am I not a Philistine, and are you not servants of Saul? Choose a man for yourselves, and let him come down to me.
Goliath's explanation may be due to the fact that the custom was imported from the Greek world and thus the people of Israel (and other nations around them) were still unfamiliar with it.
8 He stood and shouted to the ranks of Israel, “Why have you come out to draw up for battle? Am I not a Philistine, and are you not servants of Saul? Choose a man for yourselves, and let him come down to me.