For centuries highly evolved spirits have been trying to educate humans to the reality of the afterlife in many different ways. There are some cases where the hand of a medium is completely taken over by spirit and writes at a supernormal speed, in languages unknown to the medium about subjects totally outside their knowledge. This is called “automatic writing” or “psychography”. Sometimes the writing is exceptionally small or it can only be read in a mirror. Usually, it comes through complete without the need for editing.
One famous example was Brazilian physical medium Chico Xavier who, In 1932, when he was just 22, produced a 421-page book with 259 poems, signed by 56 poets, many of them famous when alive in the flesh. He went on to produce 507 books by various authors with sales of more than 50 million copies. Read more in this article by Michael Tymn.