John Chrysostom
He set aside his weapons and chose instead a shepherd's bag along with a few stones to confront that embodiment of strength.
*****
These five stones represent the Pentateuch that was bestowed upon them by God.
And he took his staff, which he had always in his hands: and chose him five smooth stones out of the brook, and put them into the shepherd's scrip, which he had with him, and he took a sling in his hand, and went forth against the Philistine.
וַיִּקַּ֨ח מַקְל֜וֹ בְּיָד֗וֹ וַיִּבְחַר־ל֣וֹ חֲמִשָּׁ֣ה חַלֻּקֵֽי־אֲבָנִ֣ים ׀ מִן־הַנַּ֡חַל וַיָּ֣שֶׂם אֹ֠תָם בִּכְלִ֨י הָרֹעִ֧ים אֲשֶׁר־ל֛וֹ וּבַיַּלְק֖וּט וְקַלְּע֣וֹ בְיָד֑וֹ וַיִּגַּ֖שׁ אֶל־הַפְּלִשְׁתִּֽי׃
One Church Father comments on this verse
He set aside his weapons and chose instead a shepherd's bag along with a few stones to confront that embodiment of strength.
*****
These five stones represent the Pentateuch that was bestowed upon them by God.
Passages read together with this verse.