A direct order is simple, didactic, and to the point. It eliminates any alternatives or ambiguity as to the ‘proper’ course of action. It is often paired with an appeal to authority (to validate the order).
Example of Propaganda: In this poster, the Ministry of Health (the authority) sends a simple order that will help keep the war effort going: “Coughs and sneezes spread diseases. Trap the germs by using your handkerchief.” The second poster sends the same message, but plays on a popular saying.