How’s this for an expression of un-Christian retributiveness?
If God wants to make my happiness complete, he will grant me the joy of seeing some six or seven of my enemies hanging from those trees. Before their death I shall, moved in my heart, forgive them all the wrong they did me in their lifetime. One must, it is true, forgive one’s enemies – but not before they have been hanged.
–Heinrich Heine, Gedanken und Überlegungen; quoted and translated in Freud, Civilization and its Discontents.
The justification for capital punishment isn’t that it is a necessary precondition for personal forgiveness.