The Aftermath. Having Promised His Daughter To David Saul Enquires About His Antecedents (1 Samuel 17:55-58).
Analysis.
a And when Saul saw David go forth against the Philistine, he said to Abner, the captain of the host, “Abner, whose son is this youth?” (1 Samuel 17:55 a).
b And Abner said, “As your soul lives, O king, I cannot tell you” (1 Samuel 17:55 b).
c And the king said, Enquire you whose son the stripling is” (1 Samuel 17:56).
b And as David returned from the slaughter of the Philistine, Abner took him, and brought him before Saul with the head of the Philistine in his hand (1 Samuel 17:57).
a And Saul said to him, “Whose son are you, young man?” And David answered, “I am the son of your servant Jesse the Beth-lehemite” (1 Samuel 17:58).
Note that in ‘a' Saul asks after David's ancestry, and in the parallel asks David himself about it. In ‘b' he asks Abner to follow the question up and in the parallel Abner does so by bringing David to Saul. Centrally in ‘c' Saul wants to know whose son the stripling is. From what ‘tree' is he stripped?
‘ And when Saul saw David go forth against the Philistine, he said to Abner, the captain of the host, “Abner, whose son is this youth?” And Abner said, “As your soul lives, O king, I cannot tell.” '
Meanwhile Saul, as he watched David go out to fight the Philistine, was mindful of the fact that he had promised his daughter to whoever defeated the Philistine, and he was thus now concerned about David's antecedents, so he turned to Abner his general and asked, ‘Whose son is this?' It had not been important who Jesse was when all Saul had been doing was employ him as a musician. And he had probably forgotten the details of David's background, if he had ever known them. He could hardly have been expected to remember the details of the families of all his servants. It was, however, a totally different matter if he was to receive him into the family. Abner's reply was that he simply did not know (emphasising that David was a nobody).
‘ And the king said, “You enquire whose son the stripling is.” '
So the king asked him to enquire into David's antecedents. The reference to a ‘stripling' has in mind the source from which David came. He was like a small strip from the parent stem.
‘ And as David returned from the slaughter of the Philistine, Abner took him, and brought him before Saul with the head of the Philistine in his hand.'
And when David returned from his defeat of Goliath, Abner took him and brought him before Saul. David was carrying the head of Goliath in his hand as an indication of YHWH's victory. In the writer's eyes this told Saul whose son he was. He was the ‘son' of YHWH Who had given him this great deliverance. He was the new anointed of YHWH.
‘ And Saul said to him, “Whose son are you, young man?” And David answered, “I am the son of your servant Jesse the Beth-lehemite.” '
As a result of Abner's action Saul was able to question him himself, and he asked him whose son he was. David answered, “I am the son of your servant Jesse the Beth-lehemite,” after which there was further conversation (1 Samuel 18:1) in which he would have given more details about himself and his family. What he did not tell him was that he was also the anointed of YHWH. That is for the reader (and listener) to know as he stands there with the head of Goliath in his hand.