1 John 2:7

Dear friends, I am not writing you a new command but an old one, which you have had since the beginning. This old command is the message you have heard.

(v7, NIV)

The commandment which is given here is an old one. His readers may think it's a new one, but John is telling them that this command he gives is actually an old one. Even when they first began following Jesus, they heard this command. This command is the command to love one another.

My command is this: Love each other as I have loved you.

(John 15:12, NIV)

This is a command Jesus gave. In addition, this is quoted from the gospel of John, the gospel account of Jesus that John himself wrote. To those he is writing, they may have also heard this command from Jesus himself or heard it from John's gospel account of Jesus. In addition, Jesus is our example for love. Jesus loved us. As followers of Jesus, we are to imitate him and walk as he did. He loved us; let us love others as he loved us. He died on the cross for our sins, displayed his love for us in his sacrificial death on the cross. This is love.

Love one another. This isn't a new thing, you have already heard it. Since you have already heard it, when John talks about it, it's nothing new. John is simply reminding us about it. Heed his words and listen to this command. Love one another.