On 1 John 5:7 Francis Turretin in the Institutes Q. XI, Sec. X writes,
“all the Greek copies have it [habent tamen omnia Exemplaria Graeca], as Sixtus Senensis acknowledges: “they have been the words of never-doubted truth, and contained in all the Greek copies from the very times of the apostles” [et in omnibus Graecis exemplaribus ab ipsis Apostolorum temporibus lecta] (Bibliotheca sancta , 2:298).
Also, earlier in his 1566 edition of the Bibliotheca Sancta, Sixtus writes the following regarding 1 John 5:7, “there has always been the undoubted truth in all Greek copies from the very times of the apostles” [indubitatæ semper veritatis suisse , & in omnibus græcis exemplaribus ab ipsis apostolorum]. Sisto (da Siena), Biblotheca Santa (Bavarian State Library: Franciscius, 1566, digitized Nov. 30, 2011), 972. 1,069 pages
Contrary to the critical orthodoxy of a single manuscript, Codex Montfortianus, (of which there are interesting questions about whether Erasmus actually referred to the manuscript at all) as grounds for the inclusion of 1 John 5:7, there is much yet to be learned for the passage’s inclusion which confirms the accuracy of Sixtus’ assessment of the passage and the reason why Turretin referenced his work. After hearing one side of a story for so long one might forget that there is always another side. What follows are two excerpts from the translator’s preface written in 1829 by William Evanson introducing the 1785 work of Francis Knittel (1721-1792) entitled, New Criticisms on the Celebrated Text, 1 John 5:7. In his preface, Evanson sets the stage for 251-page defense of 1 John 5:7’s inclusion in the New Testament. Knittel’s work is wonderful to read for the scope and quality of his scholarship.
The following material is a thimble full of Evanson’s preface, introducing the trajectory of Knittel’s writing. Research such as this is not a replacement for Scripture as autopistos, but, it is satisfying and confirming. Through the experience of learning, such research creates a fulfilling environment for the future exploration of information not yet discovered.
We pick up Evanson’s Translator’s Preface on page ix:
The entire evidence against the authenticity of 1 John V. 7. is resolvable into its absence from the majority of Greek Manuscripts, hitherto discovered and collated, which contain the First Epistle of St. John. The number of such may be, at the utmost, 150. Of these, there are only Two of very high antiquity; namely, the Codex Alexandrinus, in the British Museum; and the Codex Vaticanus, in the Vatican Library at Rome. These are supposed, by some, to have been of the 4th century. All other Greek Manuscripts, as yet discovered, are later than the 9th century. Those two omit the disputed clause. But that omission is only a negative testimony, at the best; and it is suspicious testimony, as being contemporary with the prevalence of the Arian Heresy, which unquestionably originated in the meaning severally attached to that verse by Alexander and by Arius, in the 4th century. And, moreover, it is counterbalanced, or neutralized, by antecedent and contemporary positive, i.e., affirmative testimony; because Tertullian in the 2d, and Cyprian in the 3d centuries, (who both understood the Greek Language well, and manifestly consulted the Original Text of the New Testament;) Origen, a Greek Father in the 3d century; the second Symbolum Antiochenum (published at the Council of Antioch, a.d. 341); Gregory of Nazianzen, a Greek Father; Phoebadius and Ausonius, Latins of the 4th century ; and Jerome, in his Latin Version, castigated, as he expressly says, ‘ad Gracam veritatem,’ in the same century; all either directly quote, or make such allusions to that verse, as necessarily infer its existence in the Greek Manuscripts of the New Testament then extant. Therefore, the testimony respecting 1 John V. 7. may be summed up thus :—Eight unsuspicious, positive, against Two extremely suspicious, negative witnesses. And the verdict, I feel confident, should be recorded as follows: “The verse, 1 John V. 7, being tried upon the sole testimony of Greek Manuscripts of the first four centuries—which, if it please some, we will call primary testimony,—we find, after due inquiry, that it did exist, as an integral part of the Greek New Testament, at, and antecedent to, the 4th century;” or, to use the words of Bishop Barlow, (no mean authority,) “We make no doubt it was originally there de facto; and, de jure, should be so still….”
Moving down further in the Preface, we pick up Evanson again on page xxv:
Thus then stands the External Evidence, as regards the disputed verse, under the several heads, 1st, Greek-Manuscript authorities of the first four centuries ; 2dly, Greek-Manuscript authorities from the 4th to the 16th century; 3dly, Printed Editions.
Under the first, we have the positive, or affirmative unsuspicious testimonies of Tertullian, Cyprian, Origen, the Second Symbolum Antiochenum, Gregory Nazianzen, Phoebadius, Ausonius, and the Latin Vulgate of Jerome, either directly quoting or undeniably alluding to the clause: and against them we have only the negative and suspicious testimony of two Greek Manuscripts [Codex Vaticanus and Codex Alexandrinus] of the New Testament; both confessedly Latinized, and (allowing them to have been written in the 4th century) the productions of an age in which Arianism had tainted the whole body of the Christian Church, for forty years.
Under the second, we have the affirmative unsuspicious evidence of at least two existing Greek Manuscripts of the New Testament; of all the most ancient and best Manuscripts of the Latin Vulgate (there being not one in fifty which omits the verse) ; and a large number of quotations or direct allusions to it, in the Works of Greek and Latin Fathers, from the 4th to the 16th century; —against the negative evidence of about 140 Greek Manuscripts, few more ancient than the 14th century; and the great majority belonging to the same suspicious stock, the Eastern Church. And, as it is admitted, that there are probably many thousand Greek Manuscripts of the New Testament in existence, which have never been collated or examined; as the Manuscripts employed by the Complutensian Editors have not yet been discovered, being either destroyed in the great conflagration of the Escurial 1671, or disposed of by some ignorant or dishonest Librarian, or concealed in the Library at Alcala, or possibly in the Vatican at Rome, under the apprehension of their proving unfavorable to the authority of the Vulgate; therefore, until the materials, on which a negative testimony can be admitted, be very considerably augmented in number and authenticity, the affirmative, i.e., in favor of the disputed clause, must be allowed to preponderate under this head also.
Thirdly, As to Printed Editions, the verse is contained in the Princeps Edition, by which Erasmus improved, and Stephens wholly formed, their several Editions of the New Testament; and in the genuine versions of Jerome, edited by Martianay and Vallarsius; names fully equivalent to those of the Deistical Wetstein and the Utilitarian Semler, or any of their servile imitators.
I have confined my remarks solely to the external evidence for and against this verse, and rest in the assured conviction that the former is decidedly preponderant. The Internal Evidence has been so ably and argumentatively discussed by the learned Bishop Burgess, and established on such an immoveable basis, entirely and unanswerably in favor of the verse, that the opponents of that verse have no other resource, than to thrust that species of evidence out of court altogether, and take refuge in a very convenient postulate, which has everything to recommend it —except truth. They tell us, that “no Internal Evidence can prove a clause to be genuine, where External Evidence is decidedly against it.” The falsity of this aphorism is palpable, from the whole history of Various Readings. How is any particular reading to be determined, when there are conflicting testimonies ? By the context ; —by the general scope of the author;—in short, by Internal Evidence alone. But the aphorism is not only untrue, but inapplicable in the case in question ; viz. 1 John V. 7. External Evidence is not decidedly against it: Internal Evidence is wholly in its favor: therefore it is a genuine Text of Holy Writ. One thing has deeply impressed me, in this inquiry. No satisfactory answer has ever been given to the question which naturally occurs, “How did that verse first gain admission and currency, as a text, of Scripture, if it were not so ab initio?”
Francis Antony Knittel,, New Criticisms on the Celebrated Text, 1 John 5:7, translated by William Alleyn Evanson (London: C. and J. Rivington, St. Paul’s Church-yard, J Hatchard and Son, Piccadilly, 1829, 1785), Translators Preface, ix-xi, xxv-xxviii.
 Italian convert to Christianity and anti-Talmudic agitator; born at Sienna (whence his name) in 1520; died in 1569. Besides homilies and mathematical writings, Sixtus was the author of the “Bibliotheca Sancta”(Venice, 1566), a Latin work in eight books, treating of the divisions and authority of the Bible; it contains an alphabetical index and an alphabetical list of rabbinical interpreters of the Bible. https://www.jewishencyclopedia.com › articles › 13792-sixtus-senensis
 “The Codex Alexandrinus is, notoriously, a Latinized Version. Wetstein was prohibited, by the Authorities at Amsterdam, from printing his Greek Testament from that Codex, because it conformed to the Papal Vulgate in many important passages.” (See Goezen’s Vertheidigung der Complutensischen Bibel &c. &c. Preface, p. xiii.) The Theological World is greatly indebted to the learned and laborious Rev. H. H. Baber, Librarian to the British Museum, for an exact facsimile of the Vetus Testamentum Gracum in this interesting Codex ; one of the most splendid additions to our stock of Biblical Literature, and an incomparable specimen of typographic skill.
 All the most ancient and best Manuscripts of Jerome’s Latin Vulgate contain 1 John V. 7. Not one Manuscript in fifty omits it. The majority of those in which it is omitted, contain the words “in terra” in the 8th verse. This is presumptive evidence of the existence of the 7th verse in the Originals from which they were transcribed.
 The verse, 1 John V. 7, was alleged against the Arians at the Council of Carthage, in the 5th century ; and its authenticity was not disputed by the Arian Bishops then present; nor questioned by any Arian, or other Heretic, from the 5th to the 16th century.
 At the same time, I must assert, that no amount of negative testimony can overthrow the positive evidence of those unimpeachable witnesses already adduced, as vouchers for the authenticity of 1 John V.7.