Luther's quest was to reverse the developments which had occurred under the Papacy (an institution he correctly identified as the Antichrist) and revert the Church back to how it was at the time of the Apostles - teaching only the Word of God. Luther therefore rejected all the false teachings which the popes had introduced over hundreds of years and which were contrary to the teachings of the Bible (e.g. the mass falsely viewed as a sacrifice, the false view that clergy were in essence separate and higher than the laity, the false belief that Mary and the saints could be prayed to and they could somehow exert influence with God, the false view that if you became a monk or nun you could ensure your place in heaven, the false view that salvation was partly earned by what you did rather than being entirely a gift from God accepted by faith, the false view that Peter was a pope and that that popes were the head of the Church etc etc) Luther rejected all these false teachings and wished to arrest all these developments because they were essentially soul destroying heresies which had been introduced into the Church by the father of lies the Devil.
So Luther didn't wish to develop Christianity if by that you mean introduce something new. He wanted rather only for the Word of God to reign supreme and for all man made doctrines to be abolished.