Classification of Demons was written by Peter Binsfeld, a German bishop and theologian who lived in the middle-to-late 1500s.
Content
The book was written in 1589. This book contains information on demons, notably, the identification of the seven deadly sins not simply as ideas or human vices, but as "actual devils". It was implied that this period was the last time the seven deadly sins were unleashed from hell and into earth[1].
Recent history
After the opening of the Devil's Gate in Wyoming, the Winchesters, Bobby, Tamara and Isaac encountered seven powerful demons who had escaped from Hell. After Isaac's death and the capture of one of the seven, Bobby discovered the identity of the demons by consulting Binsfeld's book and realized that they were the Seven Deadly Sins.
Behind the scenes
It is unknown if the book mentioned in the series had any differences from the real one published in real life.