First, two passages from Deuteronomy.
“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)
Vengeance is Mine, and recompense;
Their foot shall slip in due time;
For the day of their calamity is at hand,
And the things to come hasten upon them. (Deuteronomy 32:35 NKJV)
The question is not whether Israel should exact vengeance, but to always let God decide. Paul quotes the latter verse in Romans 12 in typical Hebrew fashion, provoking his readers to examine the whole passage. In Deuteronomy 32, God warns Israel not to act from their own arrogance. They had a cultural tendency to overreact to perceived insults. God will decide when the time is right for vengeance to fall on His enemies. Paul’s point is that we don’t go looking for excuses to start a feud.
This is a particular difference we have from the likes of the Pashtun, for example. They take some of the smallest insults as a grave offense and will likely carry on a vendetta, back and forth, for generations. That’s what arrogance brings. Paul did not say we must always reject violence, but that we wait on God to decide when things require violence. The notion that violence is forbidden is a long holdover from the medieval European code forced down the throats of peasants, and later the middle class, to ensure the nobles didn’t have competition from their subordinates. Violence was the divine right of nobles and royalty alone.
Jesus and Paul both said avoid violence. Yet Jesus cracked a whip in the Court of Gentiles. Obviously there’s something missing from the typical Western calculus here, because nothing in Scripture says that Jesus committed that violence from a privileged position. He always acted according to the Covenant as Moses gave it, but not as the Jewish (or Roman) leadership imagined it.
So the Lord specifically told Israel to commit genocide on Amalek (among others). We recall that Saul was punished for leaving the livestock and king of the Amalekites alive from battle (1 Samuel 15). In the Book of Esther, we encounter Haman, a descendant of Agag, the king of Amalek that Samuel had to execute. Apparently Agag had children who escaped that battle, since Saul didn’t bother to destroy their villages, either. He kept coming up short of God’s clear command to wipe them out. Thus, Esther and her kin had to deal with the same ancient threat while in Exile in Babylon.
The issue with Amalek is quite clear. Amalek was a grandson of Esau, the man who sold his birthright to Jacob for soup. Amalek absorbed the long smoldering hatred of Esau for his brother, and attacked Israel during the Exodus in a most cowardly and despicable manner. The Edomites (Edom was a nickname for Esau) themselves were no better, consistently favoring whatever enemy of Israel was attacking them at the time. But the curse of Edom took a very long time; they were eventually absorbed by the remnants of Israel. Amalek was supposed to be wiped out right after the Conquest. Failure to do so cost Israel dearly.
For you and I, the issue is listening with the heart, not the calculus of human wisdom. It’s not a question of tactics or strategy, but of the glory of God. We can discern via the convictions of our hearts when various responses to persecution are good or evil. The default is flight or tolerance, depending on the mission. On rare occasions, God will show His hand of wrath and call some of us to participate. We don’t do it for the sake of vengeance, but in obedience to the move of the Spirit in our hearts.
The glory is in our obedience, not so much combat savvy.