What does 1 Samuel 26:10 mean?

So David and Abishai came to the people by night: and, behold, Saul lay sleeping within the place of the wagons, with his spear stuck in the ground at his head; and Abner and the people lay around him.

Then Abishai said to David, “God has delivered up your enemy into your hand today. Now therefore please let me strike him with the spear to the earth at one stroke, and I will not strike him the second time.”

David said to Abishai, “Don’t destroy him; for who can stretch out his hand against Yahweh’s anointed, and be guiltless?”

Yahweh forbid that I should stretch out my hand against Yahweh’s anointed; but now please take the spear that is at his head, and the jar of water, and let us go.”

So David took the spear and the jar of water from Saul’s head; and they went away: and no man saw it, or knew it, nor did any awake; for they were all asleep, because a deep sleep from Yahweh was fallen on them.

Then David went over to the other side, and stood on the top of the mountain afar off; a great space being between them;