Nor executedst his fierce wrath upon Amalek - See 1 Samuel 15:1-9 (note) and the notes there.

Because thou obeyedst not the voice of the Lord,.... At Gilgal, as Abarbinel thinks; which is the first thing for which the kingdom was threatened to be taken from him, 1 Samuel 13:13,

nor executedst his fierce wrath upon Amalek: in sparing Agag, and the best of the cattle, 1 Samuel 15:9,

therefore hath the Lord done this thing unto thee this day; forsaken him, rent his kingdom from him, and would deliver him into the hands of the Philistines, as follows: had he been the true Samuel, he would have told him of some other sins of his, provoking to the Lord; as his slaughter of the priests at Nob, his cruel persecution of David, and especially of his asking counsel of one that had a familiar spirit at this time, of which not a word is said, and yet was the very transgression for which Saul died, 1 Chronicles 10:13.

The reason for Saul's rejection is then given, as in 1 Samuel 15:23 : "Because (כּאשׁר, according as) thou ... hast not executed the fierceness of His anger upon Amalek, therefore hath Jehovah done this thing to thee this day." "This thing" is the distress of which Saul had complained, with its consequences. ויתּן, that Jehovah may give ( equals for He will give) Israel also with thee into the hand of the Philistines. "To-morrow wilt thou and thy sons be with me (i.e. in Sheol, with the dead); also the camp of Israel will Jehovah give into the hand of the Philistines," i.e., give up to them to plunder. The overthrow of the people was to heighten Saul's misery, when he saw the people plunged with him into ruin through his sin (O. v. Gerlach). Thus was the last hope taken from Saul. His day of grace was gone, and judgment was now to burst upon him without delay.

Because thou obeyedst not the voice of the LORD, nor executedst his fierce wrath upon Amalek, therefore hath the LORD done this thing unto thee this day.

28:7-19 When we go from the plain path of duty, every thing draws us further aside, and increases our perplexity and temptation. Saul desires the woman to bring one from the dead, with whom he wished to speak; this was expressly forbidden, De 18:11. All real or pretended witchcraft or conjuration, is a malicious or an ignorant attempt to gain knowledge or help from some creature, when it cannot be had from the Lord in the path of duty. While Samuel was living, we never read of Saul's going to advise with him in any difficulties; it had been well for him if he had. But now he is dead, Bring me up Samuel. Many who despise and persecute God's saints and ministers when living, would be glad to have them again, when they are gone. The whole shows that it was no human fraud or trick. Though the woman could not cause Samuel's being sent, yet Saul's inquiry might be the occasion of it. The woman's surprise and terror proved that it was an unusual and unexpected appearance. Saul had despised Samuel's solemn warnings in his lifetime, yet now that he hoped, as in defiance of God, to obtain some counsel and encouragement from him, might not God permit the soul of his departed prophet to appear to Saul, to confirm his former sentence, and denounce his doom? The expression, Thou and thy sons shall be with me, means no more than that they shall be in the eternal world. There appears much solemnity in God's permitting the soul of a departed prophet to come as a witness from heaven, to confirm the word he had spoken on earth.