This article is a proposal of a new edition of the text of Agnus Dei contained in the manuscript kept in the Kórnik Library (manuscript No. BK 101), consisting of comprehensive transliteration, scientific transcription with linguistic commentary and - which is a significant novelty compared to the previous editions of historical texts - philological translation. The combined analysis of language and versification allowed for a fuller reading of the meaning of the text and - in consequence - the drafting of a new transliteration and transcription, in many places different from the one published by M. Muszyński in 1968. The article contains a description of the codex in which the presented text is written, a short history of the European and Polish cult of wax medallions consecrated by the Pope, as well as the Latin text of a poem about Agnus Dei, which may be the source (although not necessarily a direct one) of the Polish text.