Thank you for the question on David cutting off Goliath’s head, “Why did David cut off Goliath’s head?”
David cut off Goliath’s head to show that the Philistine’s champion is truly dead.
The Scriptures record that David stated that he will cut off the head of the Philistine’s champion head. I Samuel says this, “David said to the Philistine, “You come against me with sword and spear and javelin, but I come against you in the name of the LORD Almighty, the God of the armies of Israel, whom you have defied. 46 This day the Lord will deliver you into my hands, and I’ll strike you down and cut off your head. This very day I will give the carcasses of the Philistine army to the birds and the wild animals, and the whole world will know that there is a God in Israel. 47 All those gathered here will know that it is not by sword or spear that the LORD saves; for the battle is the LORD’s, and he will give all of you into our hands” (NIV).
As both armies were on opposing hills, the Israelites and the Philistines saw that David didn’t carry a javelin, sword, or even a bow and arrow. David carried a sling in his hand. The thought of both armies is that how will this rock knock down this giant champion. He had armor all over his body with an armor bearer before him. The odds of David defeating Goliath were improbable if not nearly impossible. It appeared that anywhere that David released his rock will just bounce off Goliath’s armor. It looks hopeless.
God guided David’s hand in swinging his rock to the nearly only vulnerable place was that forehead. Everyone saw Goliath falling down, but was he dead. He may have been daze or knocked unconscious. No one was certain at all if Goliath would get up or not.
The cutting off of Goliath’s head was to state categorically that the Philistine’s champion is dead. David’s declaration that he would cut off the head of him came true. A boy, not a warrior, was able to defeat the Philistine’s champion. The Philistine lost heart and the Israelites’ heart was strength. The battle and rout was on after the death of Goliath.
Summary: David cut off Goliath’s head to fulfilled his word and to affirm that Goliath is dead, not knock unconscious or dazed.
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