Israel and Philistines line up against each other again, and their champion Goliath defies Israel unanswered for forty days. David the delivery boy pipes up and offers to fight him, trusting God and the shepherd skills he's cultivated. He speaks in Gods name, knocks Goliath out with a sling stone, and cuts off his head with his own sword.
Goliath was just the beginning! David is made commander in chief, Jonathan's friend, and he defeats the Philistines many times. Saul is afraid of him, and angry that Israel honors David more than himself. He tries to get David killed by sending him to fight many Philistines.
How this is about Jesus
He alone could defeat the strong man and plunder his house to free us from our spiritual tyranny.
He was envied by Israel's rulers who maneuvered to get rid of Him.
Like Saul, there are times we are so envious of fellow believers, we would rather see God's enemies defeat them than see them prosper.
We need to trust God in the face of opposition, and not fight the good fight with worldly weapons.