Treatise Against the Bogomils

Sermon bears the full title Homily of the Unworthy Presbyter Cosmas Against the Newly-Appeared Bogomil Heresy (Church Slavonic: недостоинаѥго козмꙑ презвѵтера бесеѣда на новоѩвивъшѫѭ сѧ ересь богоумилоу, romanized: nedostoinajego kozmy prezvütera beseěda na novojęvivǔšǫjǫ sę eresǐ bogumilu), or, in other manuscripts, Sermon of Saint Cosmas Presbyter Against the Heretics, A Discussion and an Instruction from the Books of God.

[2] It is also an important source on life and society in 10th-century Bulgaria,[4] which is described as suffering a major crisis, the glorious days of Peter's father Simeon the Great (r. 893–927) long over.

The first section of the treatise is a vehement criticism of Bogomilism and its disobedient followers,[4][9] whom Cosmas accuses of contributing to the degradation of Bulgarian society.

[10] As Cosmas purposefully employed around 70 quotations from Apostle Paul to debunk the beliefs of Bogomils, he was very likely aware of the sect's ancestral ties to Paulicianism.

While Cosmas was a staunch supporter of the Bulgarian Orthodox Church's policies against Bogomilism, in the second section he spares no criticism to that religious body's other practices.