Where is this "scripture only" precept found in Scripture?
Who gets to decide what "the doctrine established by Scripture" is?
Who defined Scripture?
Jesus Christ was, Himself, the Word of Scripture made flesh John 1. Christ, Himself, asserted the authority of Scrpture. Matthew 26:53-56 And, of course, the role of Scripture in determining the orthodoxy of faith and practice is confirmed by the Apostle Paul. 2 Timothy 3:16-17.
Scripture is believed by Lutherans to have been determined by the early Church fathers and not to require interpretation.
Now, let me ask you. What was the Authority for the Bishop of Mainz to sell Indulgences?