Charles Ellicott Commentary 1 Samuel 17:46

"This day will Jehovah deliver thee into my hand; and I will smite thee, and take thy head from off thee; and I will give the dead bodies of the host of the Philistines this day unto the birds of the heavens, and to the wild beasts of the earth; that all the earth may know that there is a God in Israel," — 1 Samuel 17:46 (ASV)

I will smite you. —David reiterated to the Philistine, as he had done to Saul, his certainty of victory, but in the same breath said that the victory would be that God's, whose name the Philistine had just been contemptuously using.