Adam Clarke

The Lord shall smite him - He shall die by a stroke of the Divine judgment; or his day shall come to die - he shall die a natural death; which in the course of things must be before mine, and thus I shall get rid of mine enemy; or he shall descend into the battle, and perish - he shall fall by the enemies of his country. These are the three ordinary ways by which man accomplishes, as a hireling, his day. Murder David could not consider to be lawful; this would have been taking the matter out of God's hand, and this David would not do.