Saul's envy, and jealousy, and discontent revived his melancholic distemper, which the devil, according to his wont, struck in with. He prophesied, or, he feigned himself to be a prophet, for so the Hebrew verbs in Hithpahel oft signify, i.e. he used uncouth gestures, and signs, and speeches, as the prophets, or sons of the prophets, used to do; for which they were by the ignorant and ungodly sort reputed madmen, 2 Kings 9:11. And it may seem probable that Saul did now speak of Divine things politicly, that thereby he might lull David asleep, and kill him before he suspected any danger. There was a javelin in Saul's hand, which he kept there for the following purpose.
Related Commentaries of 1 Samuel 18:10
1 Samuel 18:10
10 And it came to pass on the morrow, that the evil spirit from God came upon Saul, and he prophesied in the midst of the house: and David played with his hand, as at other times: and there was a javelin in Saul's hand.