Saul’s call to war is similar to that implied in the victory song of Deborah in Judges 5; there is clearly a shared sense of ethnic belonging across the territories of Israel. Saul’s symbolic/prophetic gesture of dispatching the pieces of dismembered oxen and sending them to the Israelite-Hebrew towns elicits the expected response, and men are sent to fight from the tribal territories. What is most interesting, however, is that Saul does not have the confidence to muster the fighting men of the tribes on his own authority. He calls the tribes out in the name of ‘Saul and Samuel.’ Before the anointing of Saul it was Samuel — as a judge — who would have been expected to call the tribes to war.
It is likely that this is a reverberation of the 'worthless fellows' or 'scoundrels' in 1 Samuel 10:27 who doubted Saul’s ability to יָשַׁע ('save,' 'deliver,' or 'be victorious').
At Mizpah, when he was chosen as king, there was certainly more than a hint that he was considered a weakling or a coward (1 Samuel 10:22). In calling the people to war, then, in a time of emergency, he appeals to the authority of Samuel the judge.
It is his victory at Jabesh-gilead that ultimately secures the confidence of the people in his ability to rule. All power is negotiated; in the case of the kings of Israel, it is the king’s ability to be victorious in battle that guarantees his throne. It is noted that no one offered to kill those who doubted him at Mizpah until he proved himself in war.