Today’s Gospel is a short paragraph taken from the Sermon on the Mount, which was an address in which Jesus explained ways in which the imperfect rules of the Old Testament must give way to his own perfect rules. Some people insist that all Old Testament rules still bind us, but such people are disobeying Jesus who set those old rules aside.
That Old Testament rule about an eye for an eye and a tooth for tooth comes in Chapter Twenty-One of Exodus, which seems to be a collection of tribal laws that Moses combined with teachings he had from God. There is much in that chapter that could not have come from God. For instance it gives the rules to be followed when selling a daughter into slavery.
As well, it says that if a man beats a male or female slave so brutally that he or she dies immediately he should be punished. It goes on to say, 21. If, however, the slave survives for a day or two, he is not to be punished, since the slave is his own property.