1 Samuel 13:11

What hast thou done? — The deeper aspects of King Saul’s sin are discussed in Excursus F. On this memorable occasion the king plainly told Samuel that though he would gratefully receive any help which the prophet of the Most High could and would bring him, still, in an emergency like the present, sooner than run any risk, he preferred to act alone, and, if necessary, to go into battle without Divine consecration and blessing. The danger at this juncture was imminent; to ward it off, he considered that the direct Divine intimation which he allowed he had received through Samuel must be disregarded. Acting upon this persuasion, he set it aside, acting according to the ordinary dictates of worldly prudence. He must in his action at Gilgal either have forgotten or disbelieved the story of the Joshua conquest, and of the signal deliverances under the hero Judges, when the Glorious Arm fought by the people, and splendid successes were won in the face of enormous odds through the intervention of no mortal aid.

Saul might have been, and was, a valiant and skilful general, but was no fitting Viceroy of the invisible King in heaven, who required from him before all things the most ardent unquestioning faith.
Saul and his house, it is too clear, would only rule the Israel of God according to the dictates of their own haughty will.

The twice-repeated assertion of Samuel, “Thou hast not kept the commandment of the Lord” (1 Samuel 13:13) — an assertion uncontradicted by Saul — shows us that this whole transaction was an act of overt rebellion against the will of the Eternal.