"Abner, whose son is this young man?" Abner answers, "As your soul lives, O king, I do not know" (1 Samuel 17:55). After the fight David is brought in with the Philistine's head in his hand and says, "I am the son of your servant Jesse the Bethlehemite" (17:58). One chapter earlier, Saul had sent to Jesse for David by name and made him his armor-bearer (16:19-21).
The question is an idiom for "Who is this?", and a similar one is asked about Saul himself in 1 Samuel 10:12, when he turns up among the prophets. Set beside chapter 16, where Saul already loves David, the question reads as a sign that this telling once stood on its own. The text keeps the question and the earlier meeting side by side.
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