1 Samuel 17:25
And the men of Israel said, Have ye seen this man that is come up? surely to defy Israel is he come up: and it shall be, that the man who killeth him, the king will enrich him with great riches, and will give him his daughter, and make his father’s house free in Israel.
Goliath's coming up was a defiance of Israel, and the men of the army recognized it as a challenge meant to defy them. The Israelite army was discouraged and afraid before him, left without a champion willing to meet him in fight. Their fear and unwillingness to meet him reflected lack of trust in God.
The king promised that the man who killed him would be enriched with great riches, would be given the king's daughter in marriage, and would have his father's house made free from obligations. Saul's offer of that great reward was made because Israel was terrified and no one dared fight, reflecting Saul's own fear and inability to lead Israel with confidence in God. David saw the defiance as an insult to the armies of the living God and responded with zeal to uphold the honor of the living God and the credit of his people.
The verse warns against meeting opposition with defiance, boastfulness, and confidence in one's own strength. Ministers who provoke debate and rely on prepared arguments act like Goliath rather than humble David. By failing to trust God to give truth the victory they magnify themselves, lose balance, and harm themselves and others.