Jesus said, “You have heard that it was said, ‘You shall love your neighbor and hate your enemy’” (Matt. 5:43). This is taken from Lev. 19:18, “You shall not take vengeance or bear a grudge against the sons of your own people, but you shall love your neighbor as yourself: I am the Lord.” Notice that this command is limited only to fellows Israelites. Thus, people in Jesus’ time thought that their neighbor refers to people only of their own kind and religion. But they also thought that people outside of their ethnicity and religion should not be loved. They thought that they should love people who are good to them; but hate people who are bad to them. They should love their neighbor but hate their enemy.
Jesus said, “You have heard it said” like this. “But I say to you,” Jesus counters in v. 44. This is the true teacher of the Law rightly interpreting the Law. They have misinterpreted the Law. Now the true teacher of the Law is rightly interpreting it to them.