Saul's victory over Amalek and his defeat to himself. Saul is king. As such, the king represents the entire nation, and is essentially God's representative on Earth. The king is commanded to fulfill the national destiny to eradicate Amalek, the archetypal enemy. This war is a vendetta, it is not for booty, or for any other personal/national gain. Vendetta means total annihilation. But Saul, the king, is of another mindset. He does take booty and he wants to boast of his victory, as with all the others. As such, Saul offers to God what Saul thinks is good enough, but God has other thoughts. In spirit, Saul has committed the same offense as did Eve in Eden, Cain with his sacrifice, and as did the worshipers of the Golden Calf, by personally defining his form of obedience, as opposed to listening to and following God. Saul is rejected from being king over Israel.