Bibliomancy also called sortes biblicae, or sortes sanctorum is divination by means of the phrases in a book, especially the verses in the bible. Bibliomancy was an ancient practise, the ancients drew prognostications from the works of Homer and Virgil. In 465 the Council of Yannes condemned the practice, as did the Councils of Agde and Auxerre. But in the twelfth century we find it employed as a mode of detecting heretics, and in the Gallican Church it was long practised in the election of bishops, the installation of abbots, etc. The idea was to open a book, frequently the bible, at a random page, and without looking to point to a verse. The verse thus indicated would be applicable.
Bibliomancy was also employed as a form of trial, whereby a person suspected of witchcraft or heresy was weighed against a bible. If the bible bore down the other scale, the accused would be acquitted. It is unlikely many such unfortunate victims were acquitted.