Final answer:
David served Saul as a musician, playing the harp to soothe Saul's troubled mind.
Step-by-step explanation:
David's Role in Saul's Reign
As a young man, David served Saul as a musician, specifically playing the harp. In art, David is often depicted as a musician, sitting atop a boulder playing his harp in a pastoral setting. This portrayal reflects the biblical narrative where David used music to soothe Saul's troubled mind. It is important to note that David also served Saul in other capacities, such as being a warrior and general in Saul's army.