In Matthews’s Gospel, Jesus quotes the Book of Exodus on the subject of personal injury, which said: “But if injury ensues, you shall give life for life, eye for eye, tooth for tooth, hand for hand, foot for foot, burn for burn, wound for wound, stripe for stripe.” (Ex 21:23-25)
It may seem that these words encouraging vengeance, but on the contrary, the Book of Exodus actually limits the degree of retaliation which a person can inflict on others; i.e., if one is injured by another, the ensuing retaliation cannot surpass the originally incurred injury. These words from the Book of Exodus forbid excessive vengeance.
Jesus taught His disciples that they should go beyond what was required by the Mosaic Law. He taught His disciples that instead of seeking vengeance, they are to turn the other cheek, hand over their tunic or go the extra mile. If the expected behavior for someone who has been injured is vengeance, then His disciples are to surpass it by demonstrating unexpected charity.
In fact, Jesus tells His disciples to love their enemies. Jesus taught us to love our enemies not just in words but through His own example. In Jerusalem, Jesus did not resist those who arrested Him, those who put Him on trial, and those who beat Him, mocked Him and tortured Him. All that time Jesus turned the other cheek. Dying on the cross, Jesus showed his love for his enemies by saying: “Father, forgive them, they know not what they do. (Lk 23:34)”
Jesus’ final words in today’s Gospel are: “Be perfect, just as your heavenly Father is perfect (Mt 5:48).” In order to understand this meaning, let us turn to the Book of Leviticus, in which the Lord said to Moses: “Speak to the whole Israelite community and tell them: Be holy, for I, the LORD your God, am holy.” (Lev 19:2) Immediately following these words in Leviticus, various rules of conduct were enumerated for the Israelites to follow. It is clear to see that in the Book of Leviticus, God exhorts the Israelites to be holy, because He is Holy. In the same way, Jesus exhorts His disciples to be perfect, just as the Father in heaven is perfect. And the way they can strive to be perfect is by following Jesus’ teachings.