Theories suggest such a monumental feat would take over 20 years of dedication to complete. Something that may have been considered at the time as a monk's vow of purification, to live in isolation (recluse) for a long period of time allowing the spirit to speak through the scribe. In fact, the surrounding legend of the Codex Gigas is about a monk who broke his vows and was sentenced to a slow painful death being walled up. The monk of course did not want this to happen so he promised the monastery a book of glorification in a single night, and he is said to have offered his soul to the devil knowing such a book could not be completed in one night.
The giant book is attributed to pain and suffering to those who attain it, further bolstering along with several dark illustrations, the proclaimed title of the Devil's Bible. By owner's accounts, the book is said to have caused plague, mental illness, destruction and pain. This might be a reason why 8 of the 320 pages have vanished over the years. Since there is no evidence to where the pages went or why they were removed at all, it's truly anyone's answer. Though studies have shown the Codex Gigas quite likely was a form of life-punishment to a monk who broke monastery vows, many believe that by the illustrations and legends, the giant book is physically existing evidence of a greater power. A digitized version of the Codex Gigas is available for online browsing and examination direct from the National Library in Stockholm, which also highlights of commentaries and images associated with the translation process.