He was not trained as a soldier, so he was not used to wearing armor, especially the armor that was worn by Saul, who was the tallest man in the nation of Israel!
Ялангуяа израильчуудаас өндөр биетэй Саул шиг хүний хуягийг өмсөхөд амаргүй байсан биз ээ (1 Самуел 9: 2).