1 Samuel 16:21

The difficulty of reconciling this verse with 1 Samuel 17:55, is met thus: The words here are the ultimate sequence of David’s first visit to Saul, and of his skill in music, and are therefore placed here; but they did not really come to pass until after David’s victory over Goliath (see 1 Samuel 18:2). It is quite conceivable that if David had only played once or twice to Saul, and then returned to his father’s house for some months, Saul might not recognize him.