For this is the gospel message that you have heard from the beginning: that we should love one another, not like Cain who was of the evil one and brutally murdered his brother. And why did he murder him? Because his deeds were evil, but his brother’s were righteous. Therefore do not be surprised, brothers and sisters, if the world hates you. We know that we have crossed over from death to life because we love our fellow Christians. The one who does not love remains in death.
(1Jn 3:11-14 NET.)
Dear friends, I am not writing a new commandment to you, but an old commandment which you have had from the beginning. The old commandment is the word that you have already heard. On the other hand, I am writing a new commandment to you which is true in him and in you, because the darkness is passing away and the true light is already shining. The one who says he is in the light but still hates his fellow Christian is still in the darkness. The one who loves his fellow Christian resides in the light, and there is no cause for stumbling in him.
(1Jn 2:7-10 NET.)
Now this is his commandment: that we believe in the name of his Son Jesus Christ and love one another, just as he gave us the commandment.
(1Jn 3:23 NET.)
But now I ask you, lady (not as if I were writing a new commandment to you, but the one we have had from the beginning), that we love one another. (Now this is love: that we walk according to his commandments.) This is the commandment, just as you have heard from the beginning; thus you should walk in it.
(2Jn 1:5-6 NET.)