Pseudo-Jerome, Prologue to the Catholic Epistles
Many Vulgate manuscripts, including the Codex Fuldensis, the earliest extant Vulgate manuscript, include a Prologue to the Canonical Epistles referring to the comma.
If the letters were also rendered faithfully by translators into Latin just as their authors composed them, they would not cause the reader confusion, nor would the differences between their wording give rise to contradictions, nor would the various phrases contradict each other, especially in that place where we read the clause about the unity of the Trinity in the first letter of John. Indeed, it has come to our notice that in this letter some unfaithful translators have gone far astray from the truth of the faith, for in their edition they provide just the words for three [witnesses]—namely water, blood and spirit—and omit the testimony of the Father, the Word and the Spirit, by which the Catholic faith is especially strengthened, and proof is tendered of the single substance of divinity possessed by Father, Son and Holy Spirit.77[97]
The Latin text is online.[98] The Prologue presents itself as a letter of Jerome to Eustochium, to whom Jerome dedicated his commentary on the prophets Isaiah and Ezekiel. Despite the first-person salutation, some claim it is the work of an unknown imitator from the late fifth century.[3] (The Codex Fuldensis Prologue references the Comma, but the Codex's version of 1 John omits it, which has led many to believe that the Prologue's reference is spurious.)[99] Its inauthenticity is arguably stressed by the omission of the passage from the manuscript's own text of 1 John, however that can also be seen as confirming the claim in the Prologue that scribes tended to drop the text
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