Matthew 5:44–45 (ESV) … “But I say to you, Love your enemies and pray for those who persecute you,so that you may be sons of your Father who is in heaven. For he makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust.”
Jesus calls his disciples to live to a much higher standard. They are to perfectly manifest the love God has for all people, even toward their own enemies. The love demanded here has nothing to do with reciprocity relationships; rather it is a matter of giving with no thought of return.
Furthermore, God the Father is characterized as an indiscriminate lover and blesser of both the evil and the good, giving them both the sun and the rain they need to provide them with crops and sustenance.
We must love our enemies. “But I tell you: Love your enemies.” How are we to do this? We must first notice that Jesus does not ask us here, nor has he ever asked us, to love our enemies in the same way that we love our loved ones—our nearest and dearest. There are people for whom we have a spontaneous, natural, instinctive love. We do not have to make any effort to love them—we just do. Jesus is not asking us to have a romantic love or a buddy love or a family love or an emotional love for our enemies. What he commands is an agape love—that is, a deliberate, intelligent, determined love—an invincible goodwill toward them.
The best illustration I know of to explain what Jesus is talking about comes from the life of one of my wife’s dearest friends. She and her family had just returned from the mission field and had rented a rather nice townhouse—at least it was very nice compared to what they’d had on the mission field. She is a very creative person and did a wonderful job of decorating the place, and they settled in. Only one thing was wrong—the family who moved in next door. They turned the front yard into a desert, broke the windows out of their house, were always using foul language, urinated in the front yard, and generally caused havoc in the neighborhood. The final straw was when one of the boys climbed into our friends’ yard and threw a whole can of orange paint over the patio walls. My wife’s friend was really angry. She did not like her neighbors. She was not happy with the Lord for putting her where he had put her. Realizing that her heart was not right, she got down on her knees and said, “Lord, you know that I do not like these people at all. God, help me to love them.” She did not feel any different, but she resolved to exercise love. She baked her neighbors a pie and took it to them, thus beginning a caring relationship. Those neighbors did not change, but she did. She had begun to love them. When those neighbors moved away, she wept. What an example of intelligent, volitional love that says, “I will love by the grace of Christ within me.”
C. S. Lewis wrote in Mere Christianity:
The rule for all of us is perfectly simple. Do not waste your time bothering whether you “love” your neighbor; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him. If you injure someone you dislike, you will find yourself disliking him more. If you do him a good turn, you will find yourself disliking him less.… The difference between a Christian and worldly man is not that the worldly man has only affections or “likings” and the Christian has only “charity.” The worldly man treats certain people kindly because he “likes” them; the Christian, trying to treat every one kindly, finds himself liking more and more people as he goes on—including people he could not even have imagined himself liking at the beginning.
That is something of the “more” that makes the true believer different from the world. It is within reach of everyone who is indwelt by the Spirit of Christ. If you are a believer, you can do it. If you are a believer, you are commanded to love like this.
 Hughes, R. K. (2001). The sermon on the mount: the message of the kingdom (pp. 143–144). Wheaton, IL: Crossway Books.