18 Because you didn’t obey Yahweh’s voice, and didn’t execute his fierce wrath on Amalek, therefore Yahweh has done this thing to you today.
1 Samuel 28:18 Cross References - WEB
1 Samuel 13:9
9 Saul said, “Bring the burnt offering to me here, and the peace offerings.” He offered the burnt offering.
1 Samuel 15:9
9 But Saul and the people spared Agag, and the best of the sheep, of the cattle, and of the fat calves, and the lambs, and all that was good, and were not willing to utterly destroy them; but everything that was vile and refuse, that they destroyed utterly.
1 Samuel 15:20
20 Saul said to Samuel, “But I have obeyed Yahweh’s voice, and have gone the way which Yahweh sent me, and have brought Agag the king of Amalek, and have utterly destroyed the Amalekites.
1 Samuel 15:23-26
23 For rebellion is as the sin of witchcraft, and stubbornness is as idolatry and teraphim. Because you have rejected Yahweh’s word, he has also rejected you from being king.”
24 Saul said to Samuel, “I have sinned; for I have transgressed the commandment of Yahweh, and your words, because I feared the people, and obeyed their voice.
25 Now therefore, please pardon my sin, and turn again with me, that I may worship Yahweh.”
26 Samuel said to Saul, “I will not return with you; for you have rejected Yahweh’s word, and Yahweh has rejected you from being king over Israel.”
1 Kings 20:42
42 He said to him, “Yahweh says, ‘Because you have let go out of your hand the man whom I had devoted to destruction, therefore your life will take the place of his life, and your people take the place of his people.’”
1 Chronicles 10:13
13 So Saul died for his trespass which he committed against Yahweh, because of Yahweh’s word, which he didn’t keep; and also because he asked counsel of one who had a familiar spirit, to inquire,
Psalms 50:21-22
Jeremiah 48:10
10 “Cursed is he who does the work of Yahweh negligently; and cursed is he who keeps back his sword from blood.