Sayings of the Holy Fathers:

A brother questioned Abba Poemen in these words, "What does the Scripture mean: 'See that none of you repays evil for evil?'" The old man said to him, "Passions work in four stages: first, in the heart; secondly, in the face; thirdly, in words; and fourthly, it is essential not to render evil for evil in deeds. If you can purify your heart, passion will not come into your expression; but if it comes into your face, take care not to speak; but if you do speak, cut the conversation short in case you render evil for evil."

The Desert Fathers

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God is not the cause of evil. He has given men knowledge and understanding, the power of discriminating between good and evil, and free will. It is man's negligence and indolence that gives birth to evil passions, while God is in no way the cause.

St. Antony the Great