The publication brings into scholarly circulation the recently identified interpretation of the liturgy under the title Протль лургїи, и црк҃ви, и чи́н сщ҃енничьском, which is known in two manuscripts of Serbian origin, 16th century: RGADA 88 (84r – 87r) and in Bogisic 52 (122v21, 133r-v, 124r-v. Based on specific differences in the text, it has been established that the work is a summary translation of the treatise ‘Ἑρμηνεία περὶ τοῦ θείου ναοῦ’ by the Byzantine theologian Simeon of Thessalonica (1381/1387–1429). The Slavic translator did not leave his name. It is assumed that the prototype of the codices is a medieval Serbian manuscript from the first half of the 15th century, created in the circle of scribes under the patronage of the despot Stefan Lazarević and that Konstantin Kostenečki, also called the Philosopher, made the translation of the text. He was a Bulgarian intellectual in exile, who worked in the court of the mentioned despot. The main argument in favour of this assumption is that the interpretation of the liturgy in the two collections appears in the context of works confirmed in paleo-Slavic studies as coming from the pen of Constantine.