Explain why the development of printing was described as a "revolution."
Before the Gutenberg's invention of moveable type, books were scarce and very expensive. They had to be copied by hand. Without books, most people didn't learn to read. Printing enabled anyone to write pamphlets and books and distribute them. Since more people had access to printed materials, more people became literate.
As with all new technology, there were nay-sayers. Some complained that being able to read destroyed people's memories. They didn't need to remember stories, poems, events because they could read about them.