Charles Ellicott Commentary 1 Samuel 17:9

"If he be able to fight with me, and kill me, then will we be your servants; but if I prevail against him, and kill him, then shall ye be our servants, and serve us." — 1 Samuel 17:9 (ASV)

Then will we be your servants. —Each of the positions which the two opposing armies held was nearly impregnable; thus, it seemed as if a single combat was the only way of deciding the present campaign: moreover, in those ancient times, such single combats between renowned chieftains of the opposing armies were by no means uncommon. The reader of the Iliad will always readily recall—in dialogues before the deadly duel—words not entirely unlike the haughty, boastful challenge of the giant Philistine. See, for instance, the speeches of Glaucus and Diomede in Book VI of the Iliad: “Come here,” says Glaucus, “that you may quickly reach the goal of death.”