Some argue that the Bible is contradictory concerning the question, “Did Saul know who David was?” The argument is that 1 Samuel 16:19-23 shows that Saul knew who David was, but 1 Samuel 17:55-58 says that Saul did not know who David was. However, there are several possible explanations for this alleged contradiction in the Bible.
19 Therefore Saul sent messengers to Jesse and said, “Send me David your son, who is with the sheep.” 20 And Jesse took a donkey laden with bread and a skin of wine and a young goat and sent them by David his son to Saul. 21 And David came to Saul and entered his service. And Saul loved him greatly, and he became his armor-bearer. 22 And Saul sent to Jesse, saying, “Let David remain in my service, for he has found favor in my sight.” 23 And whenever the harmful spirit from God was upon Saul, David took the lyre and played it with his hand. So Saul was refreshed and was well, and the harmful spirit departed from him.1 Samuel 16:19-23
55 As soon as Saul saw David go out against the Philistine, he said to Abner, the commander of the army, “Abner, whose son is this youth?” And Abner said, “As your soul lives, O king, I do not know.” 56 And the king said, “Inquire whose son the boy is.” 57 And as soon as David returned from the striking down of the Philistine, Abner took him, and brought him before Saul with the head of the Philistine in his hand. 58 And Saul said to him, “Whose son are you, young man?” And David answered, “I am the son of your servant Jesse the Bethlehemite.”1 Samuel 17:55-58
1 Samuel 17:55-58 does not say that Saul did not know who David was. In this passage, Saul asks David whose son he was. It is reasonable to believe that either Saul did not know the name of David’s father, or had forgotten who David’s father was.
There are some foundational principles that apply to all alleged and apparent contradictions in the Bible. To read more, see Bible Difficulties: Foundational Principles.
To read more answers to alleged and apparent contradictions in the Bible, see “Contradictions” in the Bible Answered.
These books are also excellent resources: