His love is the reason
19 We love each other because he loved us first. 20 If someone says, “I love God,” but hates a fellow believer, that person is a liar; for if we don’t love people we can see, how can we love God, whom we cannot see? 21 And he has given us this command: Those who love God must also love their fellow believers. (1 John 4:19-21, NLT)
To say you love chocolate, but never eat it is a bit of a contradiction... Or to say you love a show that you never watch, or love a certainty type of music, but never listen to it are both examples of how actions can belie the stated affection.
Similarly, our actions towards one another will either confirm our love for God or deny it. If we really love God, His family will become the place in which we actualise this love. To love one another is a commandment, not an optional extra. Because God loved us, we are commanded to show the same love for each other.