1 Samuel 19:20

Over them — To instruct and direct them in those holy exercises. For though they prophesied by Divine inspiration, yet they were both to prepare themselves for it before hand, and to make good improvement of it afterwards, in both which they needed Samuel's counsel and assistance. And whereas some might falsely pretend to those raptures; or the devil might transform himself into an angel of light, Samuel's presence and judgment was necessary to prevent and to detect such impostures. Besides, Samuel would by his present conjunction with them in those holy exercises, encourage them, and stir up others to the coveting of those gifts, and to the performance of such religious duties. Prophesied — Being inspired by God as Balaam was; that being wrapt up into such an extasy, their minds might be wholly taken off from their design of seizing David.