What does 1 Samuel 17:36 mean?

David is at the Israelite army camp speaking to King Saul. The young man has come from Bethlehem to deliver food to his brothers (1 Samuel 17:17–18). He has discovered that Israel's army is being challenged to champion warfare and no one is willing to fight (1 Samuel 17:8–11, 24). David views this as a reproach on Israel; a Philistine has no standing to defy the armies of the living God (1 Samuel 17:26). David has also volunteered (1 Samuel 17:32).

Now David is answering the king's objection that he is too young and inexperienced in battle to take on a battle-hardened warrior as big and imposing as Goliath (1 Samuel 17:4–7) in one-on-one combat (1 Samuel 17:33). David has described to Saul the lions and bears that would sometimes attack as he was watching his father's sheep. He did not back down when they grabbed one of the lambs. He chased the animal down and struck it until it released the sheep, and he killed the predator if it fought back (1 Samuel 17:34–35).

Now David sums it up for the king. He is not inexperienced. Goliath will not be any different than the lions and bears he has killed. The concern should not be that Goliath is a killing machine. It's that the "uncircumcised Philistine" has defied the armies of the living God. David's point is that the battle with Goliath is more spiritual than physical. The living God will defend His own name and bring judgment on Goliath for so brashly defying and shaming His army.

David may be brave, but it is his faith in God that is truly impressive. It's not that he thinks himself a better fighter than the giant, it's that he is confident the Lord will use any willing man to carry out His plan and purpose. This is the key lesson of this story: not that God provided a supernatural miracle, but that He wanted someone to act in simple faith.