Which technical advance contributed most to martin luther's success in northern europe?

The printing press

Movable type printing was introduced to Europe by Johann Gutenberg in the mid-15th century.  This technological advance made it possible for a reformer like Martin Luther to spread his ideas widely and rapidly.  While overall literacy rates were low at that time, it was common for people to gather for reading of the latest Reformation materials.  Hundreds of thousands of copies of tracts written by Luther were printed and distributed -- as well as similar spread of ideas by publishing done by other reformers.