Editorial headnote: Turretin's dedicated 1674 disputation on the heavenly witnesses is a separate work. The following passages locate and translate his related treatment within the Institutio theologiae elencticae. They should be published alongside, not confused with, the 1674 disputation.
The first passage belongs to Locus II, “On Holy Scripture,” Question XI, “On the Purity of the Sources,” section X. The second belongs to Locus III, “On the One and Triune God,” Question XXV, sections IX–X. The present renderings are made directly from the Latin and preserve Turretin's own historical arguments as his arguments.
Locus II, Question XI, section X
It is falsely asserted that the Hebrew edition of the Old Testament and the Greek edition of the New are mutilated; nor can the testimonies brought forward by the adversaries prove it.
Not the history of the adulteress in John viii. For although it is lacking in the Syriac version, it is found in all Greek copies.
Not the saying in 1 John v. 7. For though some of old called it into doubt, and heretics do so still, yet all Greek copies have it, as Sixtus of Siena acknowledgeth. These words have ever been of undoubted truth and have been read in all Greek copies from the very times of the Apostles.
Not the end of Mark xvi, which may have been wanting in some copies in Jerome's time, as he himself affirmeth. Yet it is now found in all, even in the Syriac version, and is plainly necessary for carrying forward the history of Christ's resurrection.
Locus III, Question XXV, section IX
Thirdly, the point is proved from 1 John v. 7, where three are expressly named and are said to be one: “There are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.”
Three witnesses are here set down; not qualities, but persons. For as the Father is a person, so also are the Word and the Spirit, who are placed in the same order and degree. They are witnesses not human or angelic, for their testimony is called divine in verse 10 and is therefore opposed to testimony that is human and created.
Yet they bear witness distinctly in such a manner that they are one: not by consent and will only, but by essence, even as the Father and the Son are said to be one in John x. 30.
In vain do the adversaries, that they may turn aside the edge of this weapon, labour to bring the credit of the passage into question, as though it were adulterate: because it is wanting in divers Greek copies, is not read in the Syriac and Arabic translators, and is omitted by divers Fathers.
For the most ancient and approved copies which retain the place make for us. Jerome, in the prologue to the Canonical Epistles, observeth that it stood in Greek copies; and Erasmus acknowledgeth that it was found in a most ancient British codex. The most praiseworthy editions—the Complutensian, the Antwerp, that of Arias Montanus, Robert Estienne, and Walton—which made use of the best copies, contain it.
Whence, if it be wanting in some, this must be ascribed either to the fraud and evil purpose of the Arians, as Jerome acknowledgeth, or to earlier heretics, whose sacrilegious hands are known to have been laid upon the Scriptures.
Add unto this the connection of the text itself and the course of the Apostle's discourse, which require it. For the following words, “And there are three that bear witness in earth,” would have no sense unless three witnesses, bearing witness in heaven, had first gone before, with whom the witnesses in earth might be compared.
Locus III, Question XXV, section X
They are likewise greatly mistaken who would have the passage speak of unity of consent only, or homonoia.
First, perfect concord presupposeth also consubstantiality. Therefore those among us who refer the words to consent do not exclude, but suppose, identity of nature. For whatsoever is not God, being mutable and fallible, and therefore capable of failing, can neither bear a divine testimony nor be said to be one with God.
Secondly, the heavenly witnesses are not said merely to be eis to auto, “unto the same thing,” as the earthly witnesses are said to be—a phrase which may suitably be referred to agreement—but to be to hen, “the one,” which properly inferreth identity of nature.
Nor doth it follow, because believers are said in John xvii. 21 to be one as the Father is one with the Son, that the ground of unity is the same in both. The word kathos, “as,” doth not always signify equality, but any analogy or likeness whatsoever, as in 1 Peter i. 19 and Matthew v. 48.
Neither are believers said to be one with God, but to be one spirit, 1 Corinthians vi. 17. This is not essential unity, but mystical and spiritual unity. To be one spirit is to be one in the Spirit, because the same Spirit worketh both in the Head and in the members.
Source note
Translated from Francis Turretin, Institutio theologiae elencticae, Locus II, Question XI, section X, p. 104; and Locus III, Question XXV, sections IX–X, pp. 240–241, in the 1847 Latin edition. A public-domain copy is available through Internet Archive: https://archive.org/stream/institutiotheolo01turr/institutiotheolo01turr_djvu.txt.