from 1 John 2:7-8:
“Dear friends, I am not writing you a new command, but an old command that you have had from the beginning. The old command is the message you have heard. Yet I am writing you a new command, which is true in Him and in you, because the darkness is passing away and the true light is already shining.”
The command here is “to love another.” It’s not explicitly stated, but like the unseen current propelling a ship towards its destination, this command to love invisibly pushes much of chapter 2 toward its goal. (Verses 9-10 relate response to this command as involving either hatred or love of the brother, as further proof.)
But as John says, this is not a new command. From Genesis 4 where Cain asked “Am I my brother’s keeper?” the essence of Scripture from the Law to the Prophets to Christ’s own words is “Yes, love one another. You are responsible for your brother’s well-being.” This command is from the beginning.
But something is new about it. What? John tells us. What’s new is that this command is now true in us, because the darkness is passing away and the true light is shining. Here, one’s mind goes back to John’s Gospel where the eternal Word brought a “life that was the light of men. The light shines in the darkness and the darkness does not overcome it.” In chapter 1 of this letter, we are told that God himself is light. The light that is in the Father is manifested in the Son, the Word, Christ.
And because Christ now shines (being manifested in the Gospel they heard), the darkness is passing away, retreating like a beaten dog into a safe corner.
So what makes the old command new? The commandment has not changed but the situation has. The darkness is leaving, the light now shines. The “Not yet” is becoming the “already” bit by bit, and now in this light of Christ shown us in the victory over the darkness declared by the Gospel, we can love one another because the command is now true not only “in him” but “in us” who “remain in the light”.