Luther highly esteemed the place of preaching in the Reformation. At the same time, Luther very much opposed preachers ascending to the pulpit without proper authorization. He was most certainly an advocate of the doctrine of the priesthood of all believers, but Luther made a distinction in connection with the office of preaching. To him all Christians were priests, but only those men were to preach who had been called by God, through the mediation of the congregation, to fill the pastoral office.

Luther was critical of those who publicly addressed the people without a regular call and yet claimed authorization for doing so on the basis of being led to speak by the Holy Spirit.

Martin Luther on Preaching

Patrick Ferry
http://www.mtio.com/articles/bissar31.htm