2 John 5 & 6
And now, dear lady, I am not writing you a new command but one we have had from the beginning. I ask that we love one another. And this is love: that we walk in obedience to his commands. As you have heard from the beginning, his command is that you walk in love.
In his first letter, we learned that we, as Christians, will be known by our love for each other. True love is only possible for a believer in Christ because God is love and Jesus is the Way to God. We demonstrate our love for God by walking with Him (following His lead). If we are following Him, then we will also demonstrate His love to those around us.