John Calvin Commentary Romans 12:21

"Be not overcome of evil, but overcome evil with good." — Romans 12:21 (ASV)

Be not overcome by evil, etc. This sentence is set forth as a confirmation; for in this case, our contest is altogether with perverseness: if we try to retaliate against it, we confess that we are overcome by it; if, on the contrary, we return good for evil, by that very deed we show the invincible firmness of our mind. This is truly a most glorious kind of victory, the fruit of which is not only understood by the mind but also truly perceived, while the Lord gives success to their patience; indeed, they can wish for nothing better. On the other hand, he who attempts to overcome evil with evil may perhaps surpass his enemy in inflicting harm, but it is to his own ruin, for by acting in this way he carries on war for the devil.