By the law is the knowledge of sin [Rom 3:20], so the word of grace comes only to those who are distressed by a sense of sin and tempted to despair. - Martin Luther King Jr.

An even more basic reason why we are commanded to love is expressed explicitly in Jesus' words, "love your enemies....that ye may be children of your father which is in heaven." We are called to this difficult task in order to realize a unique relationship with God. We are potential sons of God. Through love that potentiality becomes actuality. We must love our enemies, because only loving them can we know God and experience the beauty of His holiness.

I'm concerned about a better world. I'm concerned about justice; I'm concerned about brotherhood; I'm concerned about truth. And when one is concerned about that, he can never advocate violence. For through violence you may murder a murderer, but you can't murder murder. Through violence you may murder a liar, but you can't establish truth. Through violence you may murder a hater, but you can't murder hate through violence. Darkness cannot put out darkness; only light can do that.

Darkness cannot drive out darkness: only light can do that. Hate cannot drive out hate: only love can do that.” — Martin Luther King Jr., A Testament of Hope: The Essential Writings and Speeches