Gutenberg's invention was unique (remarkable) because printing blocks had never been moveable before.
Before movable type, people used block printing, where the printer prints a whole page from one piece of metal or wood. With movable type, the printer makes a letter (A, B, C ...) from a piece of metal or wood, and can use it again and again in different words. Together, all Gutenberg's inventions made printing fast. A new block did not have to be made for every page.