10The next day a harmful spirit from God rushed upon Saul, and he raved within his house while David was playing the lyre, as he did day by day. Saul had his spear in his hand.
The prophesying in view is a reference to some kind of frenzied behaviour or activity (see also 1 Kings 18:29).1 It was actions and words that clearly showed everyone that Saul was not himself.2
10 The next day a harmful spirit from God rushed upon Saul, and he raved within his house while David was playing the lyre, as he did day by day. Saul had his spear in his hand.