Jesus said at Matt. 5:43, 44, 46:
“You heard that it was said: ‘You must love your neighbor and hate your enemy.’ However, I say to you: Continue to love your enemies and to pray for those persecuting you. For if you love those loving you, what reward do you have?”
Considering the context, the main point that Jesus was making here was for us to not to let our conduct be governed by the bad behavior of others. It is easy to love those who love you, but it is extremely difficult to love those who hate and persecute you. Jesus was making the point of not to hate just because others do. Or to get into the vicious cycle of rendering evil for evil. He was teaching us to not lower ourselves to the base standards of our enemies.
Paul said: “Return evil for evil to no one,” "But keep conquering the evil with the good.” (Rom. 12:17, 21)
For more concerning this Scripture, see these articles:
The Bible’s Viewpoint - Is It Possible to Love One’s Enemies? (g 11/09 10-11; Watchtower Online Library)
Love Your Enemies (w01 1/1 17; Watchtower Online Library)
Breaking the Cycle of Hate (g01 8/8 8-10; Watchtower Online Library)