1 Samuel 15:1

Samuel also said unto Saul, The LORD sent me to anoint thee to be king over his people, over Israel: now therefore hearken thou unto the voice of the words of the LORD.

The Lord sent Samuel to anoint Saul to be king over His people Israel, so Saul's royal authority came from God and bound him to hearken to the voice of the words of the Lord, giving divine authority to the message that followed. That reminder served to introduce a specific divine command, spoken just before the order concerning Amalek. The call to listen was especially pointed because Saul had already disregarded God's word, including a presumptuous sacrifice and a rash vow that had undermined confidence in his religious character.

Despite those failures, the Lord still spoke to Saul through Samuel and entrusted him with a definite task, leaving him opportunity to prove faithful and correct past errors. By humbly accepting reproof and returning to God he could turn failure into victory. The task was a test of obedience concerning Amalek, whether he would obey God in the commission given him. The campaign against the Amalekites was a commission from God to execute divine judgment in obedience, not an occasion for Saul or Israel to seek honor or spoil, and it was meant to show the nations that those who had defied God's sovereignty would be defeated by those they had despised. Saul failed the test by taking his own course, sparing Agag and the best of the livestock instead of striking Amalek and destroying them, and so was condemned for disobedience and came under God's wrath as an example of neglecting an assigned duty. In what followed he illustrated a pattern of denying wrongdoing until the evidence could not be denied, then offering no genuine confession while viewing himself as mistreated.