'Commandment' in the Bible

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 message which you have heard.

Again, 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 already is shining.

And this is his commandment: that we believe in the name of his Son Jesus Christ and love one another, just as {he commanded us}.

And this [is] the commandment we have from him: that the one who loves God should love his brother also.