This article deals with the manuscript of a little known Baroque sermon called 'Rurale Ivaniticum' from the Library of the Prague Crusaders. Its author is the forgotten Carmelite P. Ivanus a S. Ioanne Baptista. The main subject is the usefulness of the manuscript for the study of 18th century popular culture in Bohemia. The sermon by P. Ivanus a S. Ioanne Baptista was aimed almost exclusively at the lower class rural population. Hence the 'Rurale ivaniticum' manuscript provides quite frequent examples of didactically intended folk sayings, as well as attacks on folk demonology and oneiromancy. It is from these parts of the manuscript that a merger of scholarly and folk culture clearly emerges.