Please listen to the audio since I have not yet finished the post. I’m so sorry about this.

We pick up the story with Samuel speaking to Saul in 1 Samuel 15. God has not given up on Saul and is giving him a command, a mission, to punish Amalek for what he did to Israel. 

What did the Amalekites do to Israel?

“Remember what Amalek did to you on the way as you were coming out of Egypt, how he met you on the way and attacked your rear ranks, all the stragglers at your rear, when you were tired and weary; and he did not fear God. Therefore it shall be, when the Lord your God has given you rest from your enemies all around, in the land which the Lord your God is giving you to possess as an inheritance, that you will blot out the remembrance of Amalek from under heaven. You shall not forget.
- Deuteronomy 25:17-19 NKJV

Exodus 17:8-16 records the story of how Israel defeated Amalek in the past. Amalek was the first foe to attack the people of Israel after they had come out of Egypt as a free nation;

“A kinsman of the Israelites, Amalek nevertheless displayed the most intense hatred toward them: he inherited Esau's hostility to his brother Jacob. When other nations hesitated to harm God's chosen ones, his evil example induced them to join him in the fray. "Like a robber he waylaid Israel"; "like a swarm of locusts"; "like a leech eager for blood"; "like a fly looking for sores to feed on"; Amalek ('am laḳ = the people which licketh) hurried over hundreds of miles to intercept Israel's march:”
- Jewish Encyclopedia

The Amalekites had been the first to make war upon Israel in the wilderness; and add to this their defiance of God and their debasing idolatry, and you get the Lord, through Moses, had pronouncing this sentence upon them. It was by divine direction that the history of their cruelty toward Israel had been recorded, with the command, “you will blot out the remembrance of Amalek from under heaven. You shall not forget." Deuteronomy 25:19. 

For four hundred years the execution of this sentence had been deferred, but the Amalekites had not turned from their sins. The Lord knew that these wicked people would, if it were possible, blot out His people and His worship from the earth. Now the time had come for the sentence, so long delayed, to be executed.

Patience

Sadly, God’s forbearance toward the wicked often emboldens them in their transgression. But we should never confuse God’s patience with divine indifference or tolerance of sin. Just because God delays judgment does not me that the punishment will be any less certain and terrible.

"For the Lord will rise up as at Mount Perazim,
He will be angry as in the Valley of Gibeon—
That He may do His work, His awesome work,
And bring to pass His act, His unusual act."
- Isaiah 28:21 NKJV

To our merciful God, the act of punishment is a strange act. 

"Say to them: ‘As I live,’ says the Lord God, ‘I have no pleasure in the death of the wicked, but that the wicked turn from his way and live. Turn, turn from your evil ways! For why should you die, O house of Israel?’" Ezekiel 33:11. 

Judgment

“And the Lord passed before him and proclaimed, “The Lord, the Lord God, merciful and gracious, longsuffering, and abounding in goodness and truth, keeping mercy for thousands, forgiving iniquity and transgression and sin, by no means clearing the guilty, visiting the iniquity of the fathers upon the children and the children’s children to the third and the fourth generation.”
- Exodus 34:6, 7 NKJV (bold mine)

While God does not delight in vengeance, He will execute judgment upon the transgressors of His law. He must do this to preserve the inhabitants of the earth from absolute depravity and ruin. 

In order to save some God must cut off those who have become hardened in sin. 

"The Lord is slow to anger and great in power,
And will not at all acquit the wicked."
-Nahum 1:3 NKJV 

The very fact of God’s reluctance to execute justice testifies to the enormity of the sins that call forth His judgments and to the severity of the retribution awaiting the transgressor. By terrible things in righteousness, God will vindicate the authority of His downtrodden law.

War

This was the second-largest force under Saul’s command mentioned in the Bible, but this expedition was not to be entered upon for the purpose of self-aggrandizement; the Israelites were not to receive either the spoils of their enemies or the honor of the conquest. They were to engage in the war solely as an act of obedience to God, for the purpose of executing His judgment upon the Amalekites. 

This was to be a lesson to the surrounding nations. God intended that all nations should behold the doom of the people who had defied His sovereignty and should mark that they were destroyed by the very people whom they had despised.

Victory

God blessed Saul and the victory over the Amalekites was the most brilliant victory that Saul had ever gained. Sadly, instead of praising God for his military success Saul allowed it to rekindle the pride of heart that was his greatest peril. The divine command devoting the enemies of God to utter destruction was only partially fulfilled. God gave Saul absolute victory over the Amalekites, however, Saul chose to let one person live.

Ambitious to heighten the honor of his triumphal return by the presence of a royal captive, Saul ventured to imitate the customs of the nations around him and spared Agag, the fierce and warlike king of the Amalekites. 
- Patriarchs and Prophets p629

The people sinned in a similar way, reserving for themselves the finest of the flocks, herds, and beasts of burden, excusing their sin on the ground that the cattle were reserved to be offered as sacrifices to the Lord. That may sound pious, like they were thinking about God and in their desire to serve Him they spared the best of the animals. However, this really meant that these animals would be used as a substitute, to save their own cattle.

“This self-serving selective obedience by both Saul and those under his command represented an early attempt — repeated countless times throughout history —to pursue gain under the guise of serving God.
- Bergen, Robert D. The New American Commentary. Broadman & Holman, 1996. p169

Regret

Human regret implies a change of mind. 

God's regret implies a change of circumstances and relations. 

People may change their relation to God by complying with the conditions upon which they may be brought into the divine favor, or they may, by their own actions, place themselves outside the favoring condition; but the Lord is the same "yesterday, and today, and forever." Hebrews 13:8. 

Saul's disobedience changed his relation to God, but the conditions of acceptance with God never changed. God's requirements were still the same, for with Him "there is no variation or shadow of turning." James 1:17.

“God was grieved” that he “made Saul king.” This is an interesting phrase. The only other occasion in scripture where the Lord stated that he was “grieved” over people’s actions was before the flood. (Bergen 170)

So the LORD said, “I will destroy man whom I have created from the face of the earth, both man and beast, creeping thing and birds of the air, for I am sorry that I have made them.”
- Genesis 6:7 NKJV

God is aware and responsive to the choices made by people. We must understand that anything less than complete obedience to God’s instruction produces grief in heaven and pain and loss on earth. (Bergen 170) God did not make a mistake in choosing Saul as king, He was giving the people what they wanted, (1 Samuel 8 see my post Like Everyone Else). It was Saul who made a mistake, he rejected God and that affected how God related to him.

I find it fascinating how Samuel reacts. He does not gloat, he is not happy that the king has failed. This could have been Samuel’s big “I told you so” moment. But Samuel was grieved and cried out to the LORD all night. Samuel still wanted the king to succeed. Samuel wanted Israel to have a good king, to succeed, to flourish. Imagine what church would be like if more of its members were like Samuel. Sadly many Christians seem all too happy to see another fail.

Meanwhile, Saul

Meanwhile, Saul is busy setting up a monument for himself at Carmel.

So when Samuel rose early in the morning to meet Saul, it was told Samuel, saying, “Saul went to Carmel, and indeed, he set up a monument for himself; and he has gone on around, passed by, and gone down to Gilgal.”
- 1 Samuel 15:12 NKJV

Saul was not even aware he had done anything wrong. He was too busy making sure his great victory would be remembered by generations to come. Perhaps Saul thought that since God had made him king than God would support any decisions he made as king. Maybe Saul thought his sin was a small one, after all, he had been mostly obedient, he only left one man alive. Perhaps Saul figured God would not sweat the details, or that God would understand that Saul had only kept Agag alive in order to promote himself and his great victory. So if God wanted him to be king God would support his decision to strengthen his position as king by bringing Agag back alive.

What king Saul should have done is obeyed God to the best of his ability. The problem was not that Agag has escaped, or that he had been too powerful for Saul to defeat. The problem was that Saul chose to keep him alive. Saul deliberately chose to not completely fulfill the mission God had given him.

Obedience VS Offerings

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.”
- 1 Samuel 15:22-23 NKJV

Failures

Saul had failed to obey God, now he adds on to his faults by not confessing or repenting. Saul did not think what he did was wrong or bad, but he was afraid of what Samuel would do, and that fear motivated him to speak to make a request of Samuel. It was not sorrow for sin, but fear of its penalty, that actuated the king of Israel as he entreated Samuel, "I pray thee, pardon my sin, and turn again with me, that I may worship the Lord." 

(I still need to come back and finish this post, please listen to the audio link above)
Notes:

• If Saul had had true repentance, he would have made public confession of his sin; but it was his chief anxiety to maintain his authority and retain the allegiance of the people. He desired the honor of Samuel's presence in order to strengthen his own influence with the nation.
  - Patriarchs and Prophets page 632

• Saul could take no credit for becoming king. it was the Lord who took him from being a nobody to being king over Israel. (Bergen 171)

• The sequencing of Saul’s actions—performing acts of self-interest prior to those of devotion to God was reflective of his entire life. (Bergen 171)