 The treatise is recognised as the earliest and most complete work to tell of the nature of Bogomilism, its origins and its dualistic doctrine.As Catharism originated from Bogomilism, "Sermon Against the Heretics" is valuable as an insight into Catharism's Balkan predecessor.It is also an important source on life and society in 10th-century Bulgaria, which is described as suffering a major crisis, the glorious days of Peter's father Simeon the Great (r. 893–927) long over.