Augustine of Hippo — as excerpted in the Catena Aurea on Matthew 5:38-42

“(Serm in Mont. i. 19.) For the Lord was ready not only to be smitten on the other cheek for the salvation of men, but to be crucified with His whole body. It may be asked, What does the right cheek expressly signify? As the face is that whereby any man is known, to be smitten on the face is according to the Apostle to be contemned and despised. But as we cannot say ‘right face,’ and ‘left face,’ and yet we have a name twofold, one before God, and one before the world, it is distributed as it were into the right cheek, and left cheek, that whoever of Christ’s disciples is despised for that he is a Christian, may be ready to be yet more despised for any of this world’s honours that he may have. All things wherein we suffer any wrong are divided into two kinds, of which one is what cannot he restored, the other what may be restored. In that kind which cannot be restored, we are wont to seek the solace of revenge. For what does it boot if when smitten you smite again, is the hurt done to your body thereby repaid to you? But the mind swollen with rage seeks such assuagements.”