Saul cast the javelin - The javelin or spear was the emblem of regal authority; kings always had it at hand, and in ancient monuments they are always represented with it.
In ancient times, says Justin, kings used a spear instead of a diadem: Per ea tempora reges hastas pro diademate habebant, Hist. lib. xliii. And as spears were the emblems of supreme power, hence they were reputed as attributes of the Divinity, and were worshipped as representatives of the gods. Ab origne verum, pro Diis immortalibus veteres Hastas coluerent, ob cujus religionis memoriam, adhuc deorum simulachris Hastae adduntur. - Ibid.

And Saul cast the javelin,.... Out of his hand at David:
for he said; in his heart, determining in his mind:
I will smite David even to the wall with it; he determined to cast it with such force and violence, that it should pierce through David, and enter into the very wall, by the side of which David was:
and David avoided out of his presence twice; to escape the javelin cast at him; either he went out at the first time of its being thrown, and then came in again, when he threw it a second time at him, upon which he also withdrew; or this was one of the times, and the other some time after, of which see 1-Samuel 19:9. Abarbinel thinks, that David, while he was playing, his eyes were so fixed upon his own hands, that he was not aware of the javelin, and turned himself from Saul without intention both times, and so escaped without knowledge of it; such was the good providence of God towards him, and which, when Saul perceived, it wrought upon him, as follows.

And Saul cast the javelin - Being now quite under the power of that evil spirit. Twice - Once now, and another time upon a like occasion, 1-Samuel 19:10.