The Philistine is coming. David runs toward him, puts his hand in his bag, takes out a stone and slings it, and the giant falls on his face. Did the stone kill him? Both answers are in the chapter, side by side. The sling and stone are credited with slaying him, and then David takes Goliath’s own sword and finishes him.
The stone
And David put his hand in his bag, and took thence a stone, and slang it, and smote the Philistine in his forehead, that the stone sunk into his forehead; and he fell upon his face to the earth.
1 Samuel 17:49 (KJV)
Read only that verse and nobody has died yet. It reports a wound and a fall, and it stops there.
Slew him
So David prevailed over the Philistine with a sling and with a stone, and smote the Philistine, and slew him; but there was no sword in the hand of David.
1 Samuel 17:50 (KJV)
This is the verse behind the answer most of us learned, and it is true. Its last clause has a plain history. David had put on Saul’s armor and sword, found he could not go in them, and taken them off, and when he went out, “his sling was in his hand.” Between the two of them, the only sword was Goliath’s.
And the sword
Therefore David ran, and stood upon the Philistine, and took his sword, and drew it out of the sheath thereof, and slew him, and cut off his head therewith. And when the Philistines saw their champion was dead, they fled.
1 Samuel 17:51 (KJV)
Verse 50 sums up the victory, and verse 51 tells the finish. Judges and Samuel tell that sequence more than once: a man is struck down, and then someone finishes him. Jonathan’s enemies “fell before Jonathan; and his armourbearer slew after him.” In Judges 9 Abimelech, his skull broken by a piece of millstone a woman threw down, begs his armourbearer to finish him. And in 2 Samuel 1 an Amalekite claims he did the same for Saul: “So I stood upon him, and slew him.”
The Philistine army reacts to the finish. When they see their champion is dead, they run.
Before the stone
David had said as much beforehand. Before he threw anything, he told the Philistine, “I will smite thee, and take thine head from thee.” Then he said the line that outlasts both the stone and the sword.
And all this assembly shall know that the LORD saveth not with sword and spear: for the battle is the LORD’s, and he will give you into our hands.
1 Samuel 17:47 (KJV)
In the end a sword did finish the fight. David had already said, before the first stone, that the saving was the LORD’s, whatever weapon was in a hand.
After
Afterward David “took the head of the Philistine, and brought it to Jerusalem; but he put his armour in his tent.” When Abner brought him to Saul, he still had “the head of the Philistine in his hand.”
The chapter keeps its hard ending in. Genesis does something similar with the sevens that the ark’s familiar two-by-two count leaves out.
A question for another day
A careful reader will meet one more thing. In 2 Samuel 21:19 the King James says Elhanan “slew the brother of Goliath the Gittite,” and the words “the brother of” are printed in italics, added by the translators. First Chronicles 20:5 has “Lahmi the brother of Goliath” with nothing added. That pair raises its own question, and it does not change what 1 Samuel 17 says happened in the valley.
The sword at Nob
Both answers stand: verse 50 credits the sling and stone with slaying Goliath, and verse 51 ends him with his own sword. Before either, against a man who had defied “the armies of the living God”, David had said the battle was the LORD’s.
The sword had a later life. Running from Saul, David came to the priest at Nob and asked for a weapon, and was told there was one wrapped in a cloth behind the ephod, the sword of Goliath, whom he had slain in the valley of Elah. David took it: “There is none like that; give it me.”