Why is it called that? Well, quite frankly, it contains everything that 'he' ever said.
All He Said is the name of a tome that supposedly belonged to The Fear of Fears, an entity that has never been fully able to be identified. It was known as the Fear of Fear Itself, but this Fear has never been seen by human eyes, and only speculated. The Tome All He Said is supposedly an account of everything ever spoken by this theoretical entity.
The tome has a solid black cover, with a binding strap on it that can very easily be opened. The book releases a small force from its pages, compelling anyone that touches it to read its contents. The effects of this are as dangerous as one would assume.
Upon opening the book, the pages will go from a dulled yellow, to a bright white. The victim who read the book will suddenly be told a series of information in startling and solid conveyance, however after doing so, inevitably the reader will be destroyed, a husk left behind. The husk will be extremely powerful, deadly, and nearly immortal.
What exactly is inside the book is not entirely certain. It is known that it is written in a completely alien language to any known being, mortal or otherwise, and that the language is conveyed in such a way that the 'words' are heard rather than seen. For this reason, trying to read the book can have the effect splash onto victims nearby. It has only been notably read by one person, Elouise Volaks, with disastrous results. The book itself is totally indestructible, and will find its way to Earth should it be tossed into the ocean or sent into space, as if waiting for a new person to pick it up.
An individual, known only as "He who observed all he did", wrote down a rough explanation of what had supposedly been written into the tome. The beginning pages of the page where this note exists are the only safe place to read in the entire tome. While it does help to understand it, it unfortunately was written so verbose that understanding its meaning is lost in the messy grammar and spelling structure.
All that can be inferred is that the tome can somehow tell a person everything. With how the observer explains it, everyone will know pretty much every detail of existence itself. Beyond that, the observer states that he understood it all when he saw it, but lost it all when he awoke. "Everyone wakes to see him, we all know him, we all met him before birth, and will never meet him again in life nor death. We all want to know him, and he won't show himself to us."