John Gill Commentary 1 Samuel 17:32

"And David said to Saul, Let no man`s heart fail because of him; thy servant will go and fight with this Philistine." — 1 Samuel 17:32 (ASV)

And David said to Saul, let no man's heart fail because of
him
The Philistine, though so gigantic, mighty, and blustering: this he said within himself, so Kimchi; as David perceived the hearts of most, if not all, did, since none dared to go out and fight him, but on the contrary fled from him:

your servant will go and fight with this Philistine ;
and therefore there need be no thought, care, or concern to look out for another man.