From Albert Barnes Notes On the Bible:
1 John 5:7
For there are three that bear record in heaven ... - There are three that “witness,” or that “bear witness” - the same Greek word which, in 1Jo_5:8, is rendered “bear witness” - μαρτυροῦντες marturountes. There is no passage of the New Testament which has given rise to so much discussion in regard to its genuineness as this. The supposed importance of the verse in its bearing on the doctrine of the Trinity has contributed to this, and has given to the discussion a degree of consequence which has pertained to the examination of the genuineness of no other passage of the New Testament. On the one hand, the clear testimony which it seems to bear to the doctrine of the Trinity, has made that portion of the Christian church which holds the doctrine reluctant in the highest degree to abandon it; and on the other hand, the same clearness of the testimony to that doctrine, has made those who deny it not less reluctant to admit the genuineness of the passage.
It is not consistent with the design of these notes to go into a full investigation of a question of this sort. And all that can be done is to state, in a brief way, the “results” which have been reached, in an examination of the question. Those who are disposed to pursue the investigation further, can find all that is to be said in the works referred to at the bottom of the page. The portion of the passage, in 1Jo_5:7-8, whose genuineness is disputed, is included in brackets in the following quotation, as it stands in the common editions of the New Testament: “For there are three that bear record (in heaven, the Father, the Word, and the Holy Spirit: and these three are one. And there are three that bear witness on earth,) the Spirit, and the water, and the blood; and these three agree in one.” If the disputed passage, therefore, be omitted as spurious, the whole passage will read, “For there are three that bear record, the Spirit, and the water, and the blood; and these three agree in one.” The reasons which seem to me to prove that the passage included in brackets is spurious, and should not be regarded as a part of the inspired writings, are briefly the following:
I. It is missing in all the earlier Greek manuscripts, for it is found in no Greek manuscript written before the 16th century. Indeed, it is found in only two Greek manuscripts of any age - one the Codex Montfortianus, or Britannicus, written in the beginning of the sixteenth century, and the other the Codex Ravianus, which is a mere transcript of the text, taken partly from the third edition of Stephen’s New Testament, and partly from the Complutensian Polyglott. But it is incredible that a genuine passage of the New Testament should be missing in all the early Greek manuscripts.
II. It is missing in the earliest versions, and, indeed, in a large part of the versions of the New Testament which have been made in all former times. It is wanting in both the Syriac versions - one of which was made probably in the first century; in the Coptic, Armenian, Slavonic, Ethiopic, and Arabic.
III. It is never quoted by the Greek fathers in their controversies on the doctrine of the Trinity - a passage which would be so much in point, and which could not have failed to be quoted if it were genuine; and it is not referred to by the Latin fathers until the time of Vigilius, at the end of the 5th century. If the passage were believed to be genuine - nay, if it were known at all to be in existence, and to have any probability in its favor - it is incredible that in all the controversies which occurred in regard to the divine nature, and in all the efforts to define the doctrine of the Trinity, this passage should never have been referred to. But it never was; for it must be plain to anyone who examines the subject with an unbiassed mind, that the passages which are relied on to prove that it was quoted by Athanasius, Cyprian, Augustin, etc., (Wetstein, II., p. 725) are not taken from this place, and are not such as they would have made if they had been acquainted with this passage, and had designed to quote it.
IV. The argument against the passage from the external proof is confirmed by internal evidence, which makes it morally certain that it cannot be genuine.
(a) The connection does not demand it. It does not contribute to advance what the apostle is saying, but breaks the thread of his argument entirely. He is speaking of certain things which bear “witness” to the fact that Jesus is the Messiah; certain things which were well known to those to whom he was writing - the Spirit, and the water, and the blood. How does it contribute to strengthen the force of this to say that in heaven there are “three that bear witness” - three not before referred to, and having no connection with the matter under consideration?
(b) The “language” is not such as John would use. He does, indeed, elsewhere use the term “Logos,” or “Word” - ὁ Λόγος ho Logos, Joh_1:1, Joh_1:14; 1Jo_1:1, but it is never in this form, “The Father, and the Word;” that is, the terms “Father” and “Word” are never used by him, or by any of the other sacred writers, as correlative. The word “Son” - ὁ Υἱός ho Huios - is the term which is correlative to the “Father” in every other place as used by John, as well as by the other sacred writers. See 1Jo_1:3; 1Jo_2:22-24; 1Jo_4:14; 2Jo_1:3, 2Jo_1:9; and the Gospel of John, “passim.” Besides, the correlative of the term “Logos,” or “Word,” with John, is not “Father,” but “God.” See Joh_1:1. Compare Rev_19:13.
(c) Without this passage, the sense of the argument is clear and appropriate. There are three, says John, which bear witness that Jesus is the Messiah. These are referred to in 1Jo_5:6; and in immediate connection with this, in the argument, 1Jo_5:8, it is affirmed that their testimony goes to one point, and is harmonious. To say that there are other witnesses elsewhere, to say that they are one, contributes nothing to illustrate the nature of the testimony of these three - the water, and the blood, and the Spirit; and the internal sense of the passage, therefore, furnishes as little evidence of its genuineness as the external proof.
V. It is easy to imagine how the passage found a place in the New Testament. It was at first written, perhaps, in the margin of some Latin manuscript, as expressing the belief of the writer of what was true in heaven, as well as on earth, and with no more intention to deceive than we have when we make a marginal note in a book. Some transcriber copied it into the body of the text, perhaps with a sincere belief that it was a genuine passage, omitted by accident; and then it became too important a passage in the argument for the Trinity, ever to be displaced but by the most clear critical evidence. It was rendered into Greek, and inserted in one Greek manuscript of the 16th century, while it was missing in all the earlier manuscripts.
VI. The passage is now omitted in the best editions of the Greek Testament, and regarded as spurious by the ablest critics. See Griesbach and Hahn. On the whole, therefore, the evidence seems to me to be clear that this passage is not a genuine portion of the inspired writings, and should not be appealed to in proof of the doctrine of the Trinity. One or two remarks may be made, in addition, in regard to its use.
(1) even on the supposition that it is genuine, as Bengel believed it was, and as he believed that some Greek manuscript would still be found which would contain it , yet it is not wise to adduce it as a proof-text. It would be much easier to prove the doctrine of the Trinity from other texts, than to demonstrate the genuineness of this.
(2) it is not necessary as a proof-text. The doctrine which it contains can be abundantly established from other parts of the New Testament, by passages about which there can be no doubt.
(3) the removal of this text does nothing to weaken the evidence for the doctrine of the Trinity, or to modify that doctrine. As it was never used to shape the early belief of the Christian world on the subject, so its rejection, and its removal from the New Testament, will do nothing to modify that doctrine. The doctrine was embraced, and held, and successfully defended without it, and it can and will be so still.