'Command' in the Bible

But I say this as a concession, not as a command.

To married people I give this command (not really I, but the Lord): A wife must not leave her husband.

Now concerning virgins, although I do not have any command from the Lord, I will give you my opinion as one who by the Lord's mercy is trustworthy.

If anyone thinks he is a prophet or a spiritual person, he must acknowledge that what I am writing to you is the Lord's command.