'Command' in the Bible

he who is saying, 'I have known him,' and his command is not keeping, a liar he is, and in him the truth is not;

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.

Now this is His command: that we believe in the name of His Son Jesus Christ, and love one another as He commanded us.

And we have this command from Him: The one who loves God must also love his brother.