"Remember what Amalek did to you along the way when you came out from Egypt, how he met you along the way and attacked among you all the stragglers at your rear when you were faint and weary; and he did not fear God. Therefore it shall come about when the LORD your God has given you rest from all your surrounding enemies, in the land which the LORD your God gives you as an inheritance to possess, you shall blot out the memory of Amalek from under heaven; you must not forget." (Deut 25:17-19)So this is pretty serious. Remember; don't forget. What? Amalek.
So, who was Amalek? As it turns out, Amalek was family. Remember, Jacob was renamed Israel by God. Jacob's brother was Esau. "Timna was a concubine of Esau's son Eliphaz and she bore Amalek to Eliphaz." (Gen 36:12) Amalek, then, was a cousin of sorts of the Israelites. He was Esau's grandson.
But God said, "Remember what Amalek did to you." What did Amalek do to them? Well, you remember that story of Israel in the desert when they were complaining about not having anything to drink, right (Exo 17:1-7)? They were camped at Rephidim. God told Moses to take them to a rock at Horeb and strike it and, well, you know the rest. Water came out. And the next verse says, "Then Amalek came and fought against Israel at Rephidim." (Exo 17:8) Nice. The battle with Amalek was epic. Moses and two others went up on the hill and as long as Moses held his arms up, Israel prevailed. So Aaron and Hur (no, not Ben) had him sit on a rock and they held his hands up until the sun went down and the battle was won. The chapter ends with this. "The LORD has sworn; the LORD will have war against Amalek from generation to generation." (Exo 17:16) Bad news for Amalek.
It got worse. When the spies looked into Canaan, they reported that it was, essentially, impregnable. One of the reasons was ... you guessed it ... the Amalekites (Num 13:29). Later, when Balaam did his aborted cursing of Israel -- you know, the one where he blessed them instead -- he included a word for Amalek. "Amalek was the first of the nations, but his end shall be destruction." (Num 24:20) Thanks, Balaam, buddy. So, Amalek, for their treachery against family which constituted God's special people, stood forever under God's curse.
Eventually, after Israel was well entrenched in the land, God brought this back up. You may recall. It's one of those "hard things".
Thus says the LORD of hosts, "I will punish Amalek for what he did to Israel, how he set himself against him on the way while he was coming up from Egypt. Now go and strike Amalek and utterly destroy all that he has, and do not spare him; but put to death both man and woman, child and infant, ox and sheep, camel and donkey." (1 Sam 15:2-3)Eww, yeah, that one. What we've come to think of as genocide. Now, to be fair, it was not genocide. We know this because the text says that Saul killed everyone except the king, Agag (1 Sam 15:7-8), and soon thereafter Samuel finished him off (1 Sam 15:32-33), yet Amalekites appeared multiple times in multiple places thereafter. So it was a particular group of Amalekites Saul was sent to destroy. Still, it seems bloody. So we have to remember what God told them before. "Remember what Amalek did to you. You must not forget." It wasn't out of the blue. It wasn't small. It wasn't trivial.
Later, Amalek raided Ziklag and took everything that David and his men had, including families (1 Sam 30:1). He had to hunt them down and kill them. And around the same time, it was an Amalekite that killed King Saul (2 Sam 1:8-10). Later, in the time of Esther, it was Haman, an Agagite, who sought to kill all the Jews (Est 3:1). Agagite? Yes, an offspring of the king of the Amalekites that Saul failed to kill. It just never seemed to stop.
What's my point? Well, there are several. First, beware the danger of attacking God's people. It did not go well for Amalek. Remember Amalek. Then, when God sent Saul to begin carrying out His judgment, he failed. He failed to remember Amalek, and it did not go well for him. Remember Amalek. But something that jumps out at me over and over in the pages of Scripture is the "return on sin". Over and over again sins committed earlier come back to bite, sometimes generations away. Amalek was the son of a concubine, not a wife. That was not part of God's design. Saul failed to obey, and it was an Amalekite that killed him and an Amalekite that sought to kill the entire nation. Scripture says, "Be sure your sin will find you out." (Num 32:23) It is still true today. We think that we sin in a vacuum, that no one will know, that it won't make a difference. It will. It always does. It may be forgiven, but that doesn't mean there won't be consequences. Remember Amalek. Remember what God says to remember.
1 "Remember" here means to call to mind. It's not that He doesn't remember them anymore. It's that He doesn't bring them up anymore. God doesn't actually forget them. You couldn't, say, tell Him, "Lord, you remember that sin I confessed the other day. Well, I still feel sorry about it," and have Him go, "Wait ... what sin was that? I don't know what you're talking about" because God always knows everything.