Bless those who persecute you. Bless and do not curse.
Paul begins the enemy ethic with blessing — even those who persecute — and explicitly rules out cursing.
This verse opens the section by setting the hardest command first, on purpose.
14Bless those who persecute you. Bless and do not curse. 15Rejoice with those who rejoice; weep with those who weep. 16Live in harmony with one another. Do not be proud, but associate with the lowly. Do not be conceited. 17Do not repay anyone evil for evil. Carefully consider what is right in the eyes of everybody. 18If it is possible on your part, live at peace with everyone. 19Do not avenge yourselves, beloved, but leave room for God’s wrath. For it is written: “Vengeance is Mine; I will repay, says the Lord.” 20On the contrary, 21Do not be overcome by evil, but overcome evil with good.