Answer: The Printing Press. This simple device of the mid 15th Century allowed for changes that affect us still. For those whose did read often, it required time to have a book copied by hand, and was so incredibly costly, very few could afford even a modest library, for a book was a great luxury. With the invention of the Printing Press, which drastically lowered the cost of a book, it allowed for a degree of exchange of ideas unlike anything had before it. It affected the opinions of Philosophers, The Medical Field, The Sciences, War and the ugliness of oppression and the beauty of poetry and writings by a great many whose work was nearly lost in Time. This Press allowed for the works of the Classics, Virgilius and his brilliant “Æneid”, The works of Plutarch, “Libre Ab Urba Condita”, (The Books from the Beginning of the City) by Livii, Of Rome, a 2 Volume “Tome”, though Tome 1 one lost in antiquity, there are some remaining pieces of it reconstructed, in addendums to Tome 2, so the Idea of creating and forever preserving Thoughts and information was made real, first by the printing press.
In the beginning, the writing was nearly always in the once universal language of Latin, a language that allowed anyone who read Latin the ability to understand the work or results of experiments or whatever the writer had written regardless of the Origin of where the book was read, or where it was originally written. For over 500 years the Printing of books has enhanced the ability for those who wish to learn to be able, from A-Z, such a variety of work and works of art - which many of the earliest printed books are. Quality of printing can be extraordinary, those books on vellum have a lovely “3-D” effect over time, and the quality of printing images was a number of arts in itself.
The growth of writing and the reading of it, sharing ideas and of changing minds was a great step forward for Humanity, and our world would be a drastically changed one from what it is now without the Printing Press.