A postcard came from Mrs. O'Connor requesting, in the peremptory language customary to such communications, that Mrs. Make-Believe would please call on her the following morning before eight o'clock.
Whereas before, it was maybe 20 seconds of knocking, this time, it's just knock, knock, knock, knock, knock, knock, knock, in that same aggressive, sort of authoritative way for probably three minutes.
Jessica stiffened at the tone of command in Chani's voice, then observed the intense concentration in the younger woman and said: " At once." She went out through the hangings to send a waterman.
That doesn't mean you can never use a command form – that is, the form of the verb in English we would call the imperative, where you are, in some ways, telling someone to do something.