Saul's first act as king was his successful attack upon Nahash, king of the Ammonites, who had ordered the Gileadites to remove the injunction from the Torah barring the Ammonites from the congregation of Israel. In his next undertaking, the campaign against the Philistines, he displayed his piety. His son Jonathan had fallen under the severe ban pronounced by Saul against all who tasted food on a certain day, and Saul did not hesitate to deliver him up to death.
Jonathan's trespass was made know by the stones in the breastplate of the high priest. All the stones were bright, only the one bearing the name Benjamin had lost its brilliancy. By lot it was determined that its dimmed lustre was due to the Benjamite Jonathan. Saul desisted from his purpose of executing Jonathan only when it appeared that he had transgressed his father's command by mistake.
A burnt offering and his weight in gold paid to the sanctuary were considered an atonement for him. In the same war Saul had occasion to show his zeal for the scrupulous observance of the sacrificial ordinances. He reproached his warriors with eating the meat of the sacrifices before the blood was sprinkled on the altar, and he made it his task to see to it that the slaughtering knife was kept in the prescribed condition. As recompense, an angel brought him a sword, there being none beside Saul in the whole army to bear one.