"Why is the Black Book of Lam Esen like a coffin? Simple. Each holds the shape of our future."— Ormus(src)
The ancient sage Lam Esen studied Skatsimi magic and the effects of the Prime Evils on the mortal realm.  He also penned the origin story of Anu and Tathamet in this work. He compiled his findings in a large tome which became known as the Black Book due to its dark contents. The Viz-Jaq'taar's code is based on the contents of the tome.
When the Zakarum took over the lands of the East they removed the book as they believed it to be filled with heretical influences. Over the years, many rumors of the book's whereabouts sprung up. Eventually, the book was retrieved by a group of heroes. Its contents were later studied by Deckard Cain, who used them as the basis for his own writings on the Skatsim religion, and on the origins of Creation.