We love each other as a result of his loving us first.
References for 1 John 4:19
If someone says, "I love God," but hates a Christian brother or sister, that person is a liar; for if we don't love people we can see, how can we love God, whom we have not seen?
References for 1 John 4:20
And God himself has commanded that we must love not only him but our Christian brothers and sisters, too.