Why was printing important in bringing about social change?

In my opinion, the invention of the printing press (with movable
type) was one of the most important ever.  It allowed information to become available to many
more people.  This helped cause a great deal of social
change.

Before the printing press, it was very difficult for ideas
to be spread.  A person with an idea would have to speak it to someone else.  Or they would have
to hand write it and then have it copied by other people working by hand.  In both cases,
transmission of ideas was slow and the ideas got corrupted by being copied over and
over.

With the printing press, new ideas (like Luther's ideas that
started the Reformation) could be passed around quickly and easily.  At the same time,
information (books) became much cheaper and could be afforded by a much greater section of the
populace.  Both developments led to a population that could have access to many more ideas --
this helped allow for social change.