Two Kingdoms

There is a spiritual kingdom "through the word and without the sword, through which men might become devout and righteous, so that along with this righteousness they might receive eternal life."  The earthly kingdom, which is administered by the sword (that is, with punishments), exists "in order that they who refuse to be made devout and righteous unto life eternal shall by such earthly government be compelled to be devout and righteous before the world....  Though [God] does not reward this righteousness with life eternal, He nevertheless insists on it, in order that peace may be maintained among men; and He does reward it with temporal gifts."

Luther, WA 19, 629

in Wingren's Luther on Vocation, page 24