Often people want vengeance and revenge for injustices and wrongs done by other people to them, but they themselves want mercy when they wrong others. If you are not willing to show mercy, then you should not expect mercy in your life (Lev 19:18, Matt 6:14-15, Col 3:13). True justice is given out by God (Deut 32:35, Prov 20:22, Prov 24:29), so people should only respond in love, their enemies can be humbled into shame for how they treated others and repent. If they refuse then God will condemn them. In the meantime, we must love our enemies (Prov 25:21-22, Matt 5:43-48, Luke 6:27-28, Rom 12:14-21).
Christians are supposed to represent our God on earth as ambassadors (2 Cor 5:11-21), so when an enemy falls we are to lift them up even if they still hate us afterward, it misrepresents God to want the destruction of others, or to want vengeance. Vengeance is God’s job, ours is to show love and mercy, by forgiving people of their sins.
Jesus says to love even our enemies in Matt 5:44-48, Luke 6:27-36. Right before he says to love your enemies, in Matt 5:43 Jesus says, “You have heard the law that says, ‘Love your neighbor’ and hate your enemy.” The law doesn’t actually say “hate your enemy”, the 1st century Jews acted like it did to justify hating others like the Samaritans and Gentiles.
When asked by the Pharisees which is the greatest commandment, in Matt 22:34-40, Jesus replied, the greatest is Loving God with all of your heart, soul, and strength which is the “shema prayer” from Deuteronomy 6:4-5. The second greatest command he said, is to love your neighbor as yourself which is from Leviticus 19:18. The command to love your neighbor as yourself applies to your enemies as well. Jesus explains this in the parable of the Good Samaritan in Luke 10:25-37. The good Samaritan parable, in Luke 10:25-37, was presented by Jesus when explaining to Pharisees that loving your neighbor includes people you don’t like. This was after they asked him what to do to inherit eternal life. Jesus asked them what the law of Moses commands and they replied, “to love God, with all your heart, all your soul, all your strength (the Shema from Deut 6:5) and loving your neighbor” (Lev 19:18). Then in Luke 10:29, the Pharisee followed up with, “who is my neighbor”, because he wanted to justify his hatred towards his enemies. The Jews and Samaritans had cultural and social conflicts over religious views and ethnic heritage. So Jesus responds with the Good Samaritan parable to call out the religious leader’s hypocrisy. This parable is an illustration of a Samaritan (an enemy) who treats Jews better than Jewish leaders treat their own, and in that scenario, he would be counted as righteous for keeping the Torah, not the Jewish leaders who think they are better than everyone else.
We also find this in Proverbs 20:22 which says not to repay evil for good but rather let God fight your battles. Proverbs 24:17 says not to rejoice when your enemy falls. Finally, Proverbs 25:21-22 says if your enemies are hungry, give them food to eat, if they are thirsty, give them water to drink, and in doing so you will heap burning coals of shame on their heads, and God will reward you. This is similar to what Jesus says about how we treat people in Matthew 25:31-46.
In addition, there is an example of a command to love one’s enemies in the Torah in Exodus 23:4, which says to return or help an enemy’s ox. Surely if the Torah requires one to help an enemy’s livestock, then they are expected to help an enemy’s servant, child, or spouse in need, and even the enemy themselves, and return anything living or not living to an enemy when lost. This is an act of love towards the enemy.
Paul sums this all up in Romans 12:9-21. He says not to pretend to love others but actually show that you care. Hate what is evil and hold tightly to what is good (v9-10). Don’t be lazy is serving God, instead rejoice in confident hope, being patient and prayerful in times of trouble (v11-12). Be eager to show hospitality to God’s people in need (v13). Bless your enemies rather than curse them and love others no matter whom they are by being caring and compassionate (v14-15). Live in harmony with people rather than being too proud to associate with them and don’t be condescending (v16). Don’t pay back evil with evil, do things honorable and make peace with everyone (v17-18). In Romans 12:19-20, Paul quotes Deut 32:35, which says “vengeance is the Lord’s”. He also quotes Prov 25:21-22. Then in verse 21, Paul wrote, do not let evil conquer you, but conquer evil by doing good. This is similar to what the psalmist wrote in Psalms 109:1-5.