"You have heard that it was said, 'You shall love your neighbor and hate your enemy.' But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you, that you may be sons of your Father in heaven; for He makes His sun rise on the evil and on the good, and sends rain on the just and the unjust. For if you love those who love you, what reward have you? Do not even the tax collectors do the same? And if you greet your brethren only, what do you do more than others? Do not even the tax collectors do so? Therefore you shall be perfect, just as your Father in heaven is perfect."
-Matthew 5:43-48

There are many haters in the world. They are the ones that seek revenge all the time. Here, Jesus is explaining the reward for loving your enemies. I bet you all have heard of that saying, "You shall love your enemies," but who would? He is saying that if you love only the ones that love you, what will you benefit from that? He uses the phrase tax collectors because they take money from everyone equally, not just the ones they hate. With God's love in you, you can love your enemies and be perfect just like Him.