No Senator or Representative shall, during the Time for which he was elected, be appointed to any civil Office

America, unlike parliamentary governments, is a separation of powers system.  Each branch of government, with important exceptions, is given a particular task to do and it does only that task.  The legislature legislates, the executive executes, and the judiciary judges.  This clause says that members of Congress cannot be also part of the executive branch at the same time.  In parliamentary systems, e.g., Great Britain, the executive, the Prime Minister and his cabinet, are also members of parliament.  The highly developed separation of powers system set up by the Constitution is one of the great advances in the art of government and one of the most important concepts to grasp when trying to understand the Constitutional structure of the United States.