One of the main themes of I john is loving each other and loving your brethren. But when he begins to introduce this topic, it seems confusing because first he says that he’s not giving a new commandment, then in the next verse he says he is giving a new commandment.
The new commandment he is giving isn’t to love your brother, but for the remnant church to evaluate new doctrines and prophecies by the behaviour of the person proclaiming them.