In 1st Samuel 15:2-3, why would God order the Amalekites to be killed? To me, this indicates that God knew the future of the adults if they would have been spared.
Let’s read 1st Samuel 15:1-3, “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.’”
You are absolutely right that God knew what the FUTURE would have been for the Amalekites had He allowed them to live, but the real reason given here for their destruction was what they had done in the PAST. They were guilty of trying to wipe out the Israelites as they made their way from Egypt to the Promised Land. Let’s read what God said to Israel after they were ambushed by Amalek. “Remember what Amalek did to 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 UNDER HEAVEN. You shall not forget” (Deuteronomy 25:17-19; see also Exodus 17:14-16). We see here that Israel was told in advance that He would utterly destroy Amalek for their vicious attack upon them. He told them “You shall not forget,” but it would seem “they did forget,” for it wasn’t until Saul was anointed king that God commanded him to “utterly destroy all that they have, and do not spare them.”
If we were to read on in our chapter, we would see that Saul failed to utterly destroy them, for verse 9 tells us, “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.” In Saul’s eyes, “they were too good to destroy.” He thought that the animals that were spared could be sacrificed to God (verse 21). Yet was this what God thought about them? No! God knew that the Amalekites were an idol-worshipping people who had no fear of the true God, and they manifested their hatred of God by trying to destroy His people. They were NOT GOOD in His eyes and they, along with everything they had, deserved to be destroyed. Samuel had God’s mind in this and he told Saul, “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” (verse 22). Then he told Saul, “Bring Agag king of the Amalekites here to me” (verse 32) and then Samuel took his sword and “hacked Agag in pieces before the LORD in Gilgal” (verse 33).
Regarding your question and your thought about God knowing the future of the adults among the Amalekites, God knew that they were NOT GOOD and that they would NEVER BE GOOD. They would continue to hate Him and His people if they were allowed to be spared. The fact is there were Amalekites that escaped because of Saul’s disobedience, and it wasn’t until the days of Hezekiah that they were defeated (see 1st Chronicles 4:43). God also knew that the infants would grow up and be just like their parents; living in idolatry and hating the One true God, so in that sense it was a mercy that they were destroyed, for Scripture indicates that all infants who die are “spared eternal judgment and go to heaven because Christ died on the cross for them” (see Matthew 18:10-14 and then 2nd Samuel 12:23).
In closing, the Amalekites are a picture of all mankind outside of Christ, for Romans 3:12 declares, “There is NONE WHO DOES GOOD, NO NOT ONE.” Man is born in sin (Psalm 51:5) and practices sin (Romans 3:23). Even the so-called “best of men” are NOT GOOD, for we read in Psalm 39:5, “Verily every man at his best state is altogether vanity” (KJV). That is why Jesus told Nicodemus (a man who was “one of the best” in the eyes of men), “Most assuredly, I say to you, unless one is BORN AGAIN, he cannot see the kingdom of God” (John 3:5). God cannot “improve the sinful nature of man,” but He can give the sinner who repents and believes on the Lord Jesus Christ a NEW LIFE (see John 3:14-16; 5:24). This NEW LIFE gives man a NEW NATURE that IS GOOD for it “cannot sin” (see 1st John 3:9). Have you been born again? (DO) (542)