Samuel also said to Saul, “The LORD sent me to anoint you king over His people, over Israel. Now therefore, heed the voice of the words of the LORD. Thus says the LORD of hosts: ‘I will punish Amalek for what he did to Israel, how he ambushed him on the way when he came up from Egypt. Now go and attack Amalek, and utterly destroy all that they have, and do not spare them. But kill both man and woman, infant and nursing child, ox and sheep, camel and donkey.’”
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But Saul and the people spared Agag and the best of the sheep, the oxen, the fatlings, the lambs, and all that was good, and were unwilling to utterly destroy them. But everything despised and worthless, that they utterly destroyed.
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the word of the LORD came to Samuel, saying, “I greatly regret that I have set up Saul as king, for he has turned back from following Me, and has not performed My commandments.” And it grieved Samuel, and he cried out to the LORD all night.
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Then Samuel went to Saul, and Saul said to him, “Blessed are you of the LORD! I have performed the commandment of the LORD.”
But Samuel said, “What then is this bleating of the sheep in my ears, and the lowing of the oxen which I hear?”
And Saul said, “They have brought them from the Amalekites; for the people spared the best of the sheep and the oxen, to sacrifice to the LORD your God; and the rest we have utterly destroyed.”
Then Samuel said to Saul, “Be quiet! And I will tell you what the LORD said to me last night.”
And he said to him, “Speak on.”
So Samuel said, “When you were little in your own eyes, were you not head of the tribes of Israel? And did not the LORD anoint you king over Israel? Now the LORD sent you on a mission, and said, ‘Go, and utterly destroy the sinners, the Amalekites, and fight against them until they are consumed.’ Why then did you not obey the voice of the LORD? Why did you swoop down on the spoil, and do evil in the sight of the LORD?”
And Saul said to Samuel, “But I have obeyed the voice of the LORD, and gone on the mission on which the LORD sent me, and brought back Agag king of Amalek; I have utterly destroyed the Amalekites. But the people took of the plunder, sheep and oxen, the best of the things which should have been utterly destroyed, to sacrifice to the LORD your God in Gilgal.”
So Samuel said:
“Has the LORD as great delight in burnt offerings and sacrifices,
As in obeying the voice of the LORD?
Behold, to obey is better than sacrifice,
And to heed than the fat of rams.
For rebellion is as the sin of witchcraft,
And stubbornness is as iniquity and idolatry.
Because you have rejected the word of the LORD,
He also has rejected you from being king.”
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Samuel went no more to see Saul until the day of his death. Nevertheless Samuel mourned for Saul, and the LORD regretted that He had made Saul king over Israel.
from 1 Samuel 15

the LORD said to Samuel, “How long will you mourn for Saul, seeing I have rejected him from reigning over Israel? Fill your horn with oil, and go; I am sending you to Jesse the Bethlehemite. For I have provided Myself a king among his sons.”
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the LORD said to Samuel, “Do not look at his appearance or at his physical stature, because I have refused him. For the LORD does not see as man sees; for man looks at the outward appearance, but the LORD looks at the heart.”
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Samuel said to Jesse, “Send and bring him. For we will not sit down till he comes here.” So he sent and brought him in. Now he was ruddy, with bright eyes, and good-looking. And the LORD said, “Arise, anoint him; for this is the one!” Then Samuel took the horn of oil and anointed him in the midst of his brothers; and the Spirit of the LORD came upon David from that day forward. So Samuel arose and went to Ramah.
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the Spirit of the LORD departed from Saul, and a distressing spirit from the LORD troubled him.
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David came to Saul and stood before him. And he loved him greatly, and he became his armorbearer. Then Saul sent to Jesse, saying, “Please let David stand before me, for he has found favor in my sight.” And so it was, whenever the spirit from God was upon Saul, that David would take a harp and play it with his hand. Then Saul would become refreshed and well, and the distressing spirit would depart from him.
from 1 Samuel 16
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