Jamieson, Fausset and Brown on 2 Kings 9:4-6

4-6. So the young man ... went to Ramoth-gilead--His ready undertaking of this delicate and hazardous mission was an eminent proof of his piety and obedience. The act of anointing being done through a commissioned prophet, was a divine intimation of his investiture with the sovereign power. But it was sometimes done long prior to the actual possession of the throne (1Sa 16:13); and, in like manner, the commission had, in this instance, been given also a long time before to Elijah [1Ki 19:16], who, for good reasons, left it in charge to Elisha; and he awaited God's time and command for executing it [Poole].