Interesting to compare this section of Matthew with the corresponding section of Luke:
Matt. 5: 38-48...
"You have heard that it was said, `Eye for eye, and tooth for tooth.' But I tell you, Do not resist an evil person. If someone strikes you on the right cheek, turn to him the other also. And if someone wants to sue you and take your tunic, let him have your cloak as well. If someone forces you to go one mile, go with him two miles. Give to the one who asks you, and do not turn away from the one who wants to borrow from you.
"You have heard that it was said, `Love your neighbor and hate your enemy.' But I tell you: Love your enemies and pray for those who persecute you, that you may be sons of your Father in heaven. He causes his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous. If you love those who love you, what reward will you get? Are not even the tax collectors doing that? And if you greet only your brothers, what are you doing more than others? Do not even pagans do that? Be perfect, therefore, as your heavenly Father is perfect.
Luke 6:27-36...
"But I tell you who hear me: Love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you. If someone strikes you on one cheek, turn to him the other also. If someone takes your cloak, do not stop him from taking your tunic. Give to everyone who asks you, and if anyone takes what belongs to you, do not demand it back. Do to others as you would have them do to you."If you love those who love you, what credit is that to you? Even `sinners' love those who love them. And if you do good to those who are good to you, what credit is that to you? Even `sinners' do that. And if you lend to those from whom you expect repayment, what credit is that to you? Even `sinners' lend to `sinners,' expecting to be repaid in full. But love your enemies, do good to them, and lend to them without expecting to get anything back. Then your reward will be great, and you will be sons of the Most High, because he is kind to the ungrateful and wicked. Be merciful, just as your Father is merciful.
The message is the same in both—that the Father provides for the needs of people without regard to how they feel and act towards him; his grace is extended to all. Jesus challenges his disciples to follow the Father's example in their lives (and so, by doing what he does, be regarded as "sons"). However, notice the difference in the last verse. Matthew uses the word teleios, translated perfect, whereas Luke uses the word oiktirmos, translated merciful. To be merciful means to have regard for the needs of others, and is sometimes translated compassionate. Considering these two verses together, it looks like we can say that extending mercy or compassion to all—even those who are against the disciple—is the most mature, whole, and complete kind of action the disciple could undertake. This harmonizes well with other NT texts that speak of God's love (e. g., I Jo. 4:16, "God is love" and Jo. 3:16, "For God so loved the world...") and call for the faithful to extend love to others.
Perhaps Luke chose to use oiktirmos because he, most of any of the gospel writers, was an advocate of the poor and rejected, and wanted to be very clear about what Jesus was saying. Matthew, with a different background and choice of emphasis, looks at attaining the highest state righteousness, as if this maturity or completeness is the goal. Yet perfection and mercy are brought together in Matthew's story of the rich young man in 19:16-22...
Now a man came up to Jesus and asked, "Teacher, what good thing must I do to get eternal life?""Why do you ask me about what is good?" Jesus replied. "There is only One who is good. If you want to enter life, obey the commandments."
"Which ones?" the man inquired.
Jesus replied, " `Do not murder, do not commit adultery, do not steal, do not give false testimony, honor your father and mother,' and `love your neighbor as yourself.' "
"All these I have kept," the young man said. "What do I still lack?"
Jesus answered, "If you want to be perfect [teleios] , go, sell your possessions and give to the poor, and you will have treasure in heaven. Then come, follow me."
When the young man heard this, he went away sad, because he had great wealth.
There are a host of other issues, linguistic and philosophical, that could be discussed here if there is interest. Perhaps leolaia would come back in, or maybe narkissos, to help out.