Justin Martyr, Dialogue with Trypho 93

The things that are always and everywhere just provide all righteousness for every kind of human being, and every kind knows that adultery is evil, as are fornication, murder, and all such things. Even if everyone does them, they still sin knowingly when they act, and they are not excused — except those who have been driven by an unclean spirit and corrupted by bad upbringing, evil customs, and wicked laws, who have destroyed their natural intuitions, or rather extinguished them than merely disfigured them. One can see even such people not wanting to suffer the very things they impose on others. And in hostile consciences they reproach each other for the deeds they themselves commit. From this it seems to me that our Lord and Savior Jesus Christ spoke well when he said that all righteousness and piety are fulfilled in two commandments (Matthew 22:37-40): You shall love the Lord your God with all your heart and with all your strength, and your neighbor as yourself (Leviticus 19:18). The one who loves God with all his heart and strength, being full of godly purpose, will not honor any other god; he will even honor the angel whom God wishes to honor, the one beloved by the Lord and God. And the one who loves his neighbor as himself will wish for that neighbor the same good things he wishes for himself, for no one wishes evil for himself. Therefore, the one who loves his neighbor will both pray for and work to bring about for his neighbor the same things he desires for himself; for a neighbor of a human being is nothing else but the human — the like-feeling, rational living being, the human. Thus the whole of righteousness, divided in two toward God and toward humans, means that whoever, as the Word says, loves the Lord God with all his heart and all his strength, and his neighbor as himself, would truly be just. But you have never been shown to have either friendship or love toward God, or toward the prophets, or even toward yourselves; instead, as is evident, you have always been found to be idolaters and murderers of the just — so much so that you laid hands on the Christ himself, and to this day you persist in your evil, cursing and denying those who demonstrate that this crucified one is the Christ. Moreover, you demand that he be proven to be an enemy of God and accursed, worthy of crucifixion — which is the work of your irrational mind. For though you have had opportunities from the signs performed through Moses to understand that he is the one, you do not want to; and besides, thinking you can make us irrational, you dispute what happens to you, and you are left without words when you encounter a coherent Christian.