What does 1 Kings 20:13 mean?

Just then, a prophet came to Ahab and said, 'This is what the Lord says: Do you see this huge army? I’m going to hand them over to you today, and you’ll know that I am the Lord.' 1 Kings 20:13 - Modern Text Bible

(A prophet shows up and tells Ahab that God will give him victory, so Ahab will know who’s really in charge.)