In the early 1400s, Johannes Gutenberg debuted his movable type printing press. This caused a revolution in the distribution and preservation of knowledge in Europe.

The increase in the availability of books, and the corresponding decrease in the cost to acquire them, let to the widespread diffusion of knowledge which, in turn, has been credited with the onset of the Renaissance as ideas about technology and philosophy became more widely disseminated.

Further, the more widespread availability of the Bible itself—and its newfound accessibility in common languages, or languages other than Latin—has been credited as a driving force in the Protestant Reformation, which began less than seventy-five years after the debut of the Gutenberg press with the publication of Ninety-Five Theses by Martin Luther.

The immediate positive effect of Gutenberg's printing press was that educational and religious texts became much more widely available in Europe (I will assume that this is a positive development).

Gutenberg published his first Bible in either 1455 or 1456.  By the year 1500, there were more than one thousand printing presses using movable type in Europe.  These presses were putting out large numbers of texts.  By 1500, they had published between 8 and 10 million copies of about 40,000 different books.  (All statistics here from Jackson Spielvogel's Western Civilization7th edition, page 355.)

This allowed the spread of knowledge and helped to create a more educated and literate public.  This was the main immediate importance of Gutenberg's invention.