'Commandment' in the Bible

Brothers, I write no new commandment to you, but an old commandment which you had from the beginning. The old commandment is the word which you heard from the beginning.

Again, I write a new commandment to you, which is true in him and in you; because the darkness is passing away, and the true light already shines.

This is his commandment, that we should believe in the name of his Son, Jesus Christ, and love one another, even as he commanded.

This commandment we have from him, that he who loves God should also love his brother.