1 Samuel 17:15

And Saul's servants said unto him, Behold now, an evil spirit from God, sent as a punishment from God, troubleth thee.

But David went and returned from Saul, he went back and forth between his home and the king's court, just as Saul had need of him, to feed his father's sheep at Bethlehem, he helped out at home as much as possible, especially now that Saul had gone forth on the campaign against the Philistines. He had indeed been enrolled among Saul's armor-bearers, but he had not yet been drilled in the art of warfare as it was then practiced.