1 Samuel 17:57 Meaning

55And when Saul saw David go forth against the Philistine, he said unto Abner, the captain of the host, Abner, whose son is this youth? And Abner said, As thy soul liveth, O king, I cannot tell.

56And the king said, Enquire thou whose son the stripling is.

57And 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.

58And Saul said to him, Whose son art thou, thou young man? And David answered, I am the son of thy servant Jesse the Beth-lehemite.