Summary: Samuel relates God’s commandment to Saul to destroy the nation of Amalek. Saul raises an army to fight Amalek and is on the brink of victory when he captures and spares their king Agag. He also saves some of the choicest Amalekite flock to offer as a sacrifice to God to thank him for victory. However, God became angry and related to Samuel through a prophecy that He regretted making Saul king. His instruction had been to destroy the entire nation, not save their king or offer their sheep and bulls. After meeting with Saul, Samuel berates him for not listening to God’s word. He tells Saul that measure for measure, just as Saul rejected God, so too God has now rejected him as king. Samuel executed Agag before returning home to Ramah, while Saul returned home to Givat Shaul.
A deeper look: The narrative implies that had Saul killed King Agag, the Amalekites would have been destroyed and his mission completed. The Gemara notes that due to Agag being captured and held alive, he became the ancestor of Haman (Megilah 13a). The 16th century commentator Rabbi Shmuel Laniado explains that the night before his execution by the prophet Samuel, Agag impregnated a maidservant whose child continued the seed of Amalek (Kli Yakar on Shmuel I 15:30).
In the story of Esther, the Megillah notes that the Mordechai and Esther were from the tribe of Benjamin and are direct descendants of King Saul himself, who came from the Kish family (compare Samuel I 9:1-2 and Esther 2:5). The Gemara explains that while Mordechai is also referred to as Yehudi, from the tribe of Judah, this is because his mother was from the tribe of Judah while his father was a Benjaminite (Megillah 12b).
Rabbi Shmuel Eliezer Edels, known as the Maharsha (d. 1632) explains that one of the reasons Mordechai’s lineage is referred to in the Megillah is that their act of destroying Haman, the descendant of Agag, rectified this sin committed by Saul (Chidushei Aggadot on Megillah 12b).
Nevertheless, Saul’s downfall has been set and the beginning of the Davidic dynasty is about to begin.