1 Samuel 17:23

And as he talked with them, behold, there came up the champion, the Philistine of Gath, Goliath by name, out of the armies of the Philistines, and spake according to the same words, as he usually did; and David heard them.

And it came to pass, when the evil spirit from God was upon Saul, when he had special attacks of his affliction, when the gloomy moods were upon him, that David took an harp and played with his hand; so Saul was refreshed and was well, he found relief, and the evil spirit departed from him. David's story shows that the Lord leads His children in marvelous ways. Those who are intended for servants in His kingdom are so guided by Him that all they see, hear, learn, and experience is of value to them for their future calling.