Gutenberg did something fundamentally important: He invented the printing
press which was to cause a major explosion of literacy throughout Europe
in 1500.
Prior to that point, all "books" (mainly bibles) were hand
printed by monks laboriously and painstakingly copying page after page from
previously written pages (and hopefully, not taking "artistic liberty"
by making changes). Only the quite wealthy (and powerful archbishops) could
afford bibles.
With the invention of movable type and printing presses, one could "mass
produce" written works. Within a couple of decades, most people found
themselves either able to afford a book or knew someone who owned one. Announcements
and documents were distributed. Soon it became necessary to be literate
and literacy education was "needed" by the masses.

Some early Roman (about 30 B.C.) stone writings
discovered in Mainz. This was in an area devoted to
the history of the "printed" word in the museum.

Me with Johannes Gutenberg (I'm on the right)
He's actually dead now and this is a statue.

Some early (1400 A.D.) hand printed bibles. I got
yelled at for taking flash photographs. Of course, the guy
yelled at me in German so I couldn't really understand him!

A recreation of Gutenberg's first printing plant. He even
melted the lead to make the type.
Another highlight of the trip was a stop at a medieval castle.