Justin Martyr, First Apology 15

Concerning self-control, Jesus spoke with uncompromising clarity: anyone who looks at a woman with lustful intent has already committed adultery with her in his heart before God (Matt 5:27–28). He pressed the point further: if your right eye causes you to stumble, gouge it out and throw it away; it is far better to enter the kingdom of heaven with one eye than to keep both and be cast into eternal fire (Matt 5:29–30). He also declared that whoever marries a woman divorced from another man commits adultery (Matt 5:31–32). Then he acknowledged the reality of celibacy: some are made eunuchs by others, some are born so, and some renounce marriage for the sake of the kingdom of heaven — though not everyone can accept this calling (Matt 5:33–34).

Just as those who remarry under human law are regarded as sinners by our Teacher, so too are those who look at a woman to desire her; for God does not merely judge outward acts — he also sees the heart. Not only is the one who commits adultery in deed cast out, but also the one who desires to commit adultery, since nothing is hidden from God, not even our thoughts (Matt 5:27–28). Many men and women, disciples from childhood, have remained pure into their sixties and seventies; I pray that such chastity may appear in every kind of human being. What then shall we say of the countless multitude who turned from licentiousness when they heard these words? Christ did not call the righteous or the self-controlled to repentance, but the ungodly, the unchaste, and the unjust. He said plainly, 'I came not to call the righteous, but sinners to repentance' (Matt 5:38–42). The heavenly Father desires the sinner's repentance, not his punishment.

On the duty of loving all people, he taught: 'If you love only those who love you, what credit is that to you? Even prostitutes do as much. But I say to you: pray for your enemies, love those who hate you, bless those who curse you, pray for those who mistreat you' (Matt 5:43–48). On generosity and the rejection of display, he said: 'Give to everyone who asks, and do not turn away the one who wants to borrow. If you lend only to those you expect to repay, what is remarkable in that? Even tax collectors do the same. Do not store up treasures on earth, where moth and rust consume and thieves break in and steal; store up treasures in heaven, where neither moth nor rust destroys. What does it profit a person to gain the whole world yet forfeit his soul? Or what can anyone give in exchange for his soul? So lay up treasure in heaven, where neither moth nor rust destroys' (Matt 6:19–21).

'Be merciful and compassionate, just as your Father is merciful and compassionate; he makes his sun rise on the evil and the good, on the just and the unjust. Do not worry about what you will eat or what you will wear. Are you not worth far more than the birds and the wild animals? God feeds them. So do not be anxious about food or clothing; your heavenly Father knows you need these things. Seek first the kingdom of heaven, and all these things will be added to you. For where your treasure is, there your heart will be also' (Matt 6:25–34). 'Take care not to practice your righteousness before others to be seen by them; if you do, you will have no reward from your Father in heaven' (Matt 6:19–21).