Adam Clarke on 1 Samuel 18:11

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.