Charles Williams, written in the midst of WW2 (1942):
The conversion, where it is demanded, of the wild justice of revenge to the civil justice of the Divine City is the precise operation of the Holy Spirit towards Christ. All we need to do is attend to the goodwill, to the civility; the justice (in the personal relation) can be left to Christ. ‘Vengeance is mine; I will repay, sayeth the Lord.’ It is perhaps desirable to notice that the repayment is not limited to our enemy. We shall be unfortunate if we forget the trespasses, the debts, which our enemies desire to repay with their wild justice and are content to leave to his promise. It is important that we should be ready to forgive the Germans; it is not unimportant to recognize that many Germans (including Herr Hitler? Possibly; we do not very well know) may feel that they have much to forgive us. Many reconciliations have unfortunately broken down because both parties have come prepared to forgive but unprepared to be forgiven. Instruction is as badly needed in this as in many other less vital things; that holy light which we call humility has an exact power of illumination all its own.
(The Forgiveness of Sins, p. 113)