First let me say it's the verse 7 that was the insertion, not verse 8.
Kiddpeat, you still seem to miss the point. My point is the Canon were decided upon by fallible men, and even then they made changes later, such as regards Revelation of John. Recognizing this I realize and am willing to accept there may be other writings just as inspired of God as any of the books within the current accepted Canon of Scripture. This is something you seem to reject. Everything I put forth was in support of that point.
Instead you seem determined to go off on a tangent, alleging something I didn't do and not actually answering the point presented, instead attacking me on some other doctrinal issue (Trinity) with which I have no argument. I then tell you why you are wrong in your assumption about my doctrinal belief and yet you again insist I'm attacking a particular belief which I was not, neither in statement nor context.
I do not care what particular doctrine some insertion supports, what I do care is whether the particular passage is valid inspired scripture or an insertion. I don't know why you can't understand this, since I thought you were concerned over the validity and purity of the Scriptures too.
The particular passage, even as Isaac Newton noted, stands out as not seeming to fit the overall text to an accomplished student of Scripture. It's obvious the insertion does not have a direct correlation of equality to the previous passage.
You may find this of interest.
http://www.tegart.com/brian/bible/kjvonly/doug/1john5_7.html
1. Greek manuscripts-about 300 existing Greek manuscripts contain the book of I John. Of these manuscripts, only 4 (manuscript numbers 61, 629, 918, 231
contain the disputed words of v.7. All four are very late manuscripts (16th, 14th or 15th, 16th, and 18th centuries A.D. respectively); none gives the Greek text exactly as it appears in printed Greek NTs, and all 4 manuscripts give clear evidence that these words were translated into Greek from Latin.
Four additional manuscripts (88, 12th century; 221, 10th; 429, 16th; 636, 15th) have the disputed words copied in the margin by much later writers.
2. Ancient writers: no Greek-speaking Christian writer before the year 1215 A.D. shows any knowledge of the disputed words. Not once are these words quoted in the great controversy with the Arians (over the Deity of Christ and the doctrine of the Trinity) in the 3rd and 4th centuries; they certainly would have been quoted if they had existed in any Greek manuscript of that period.
The disputed words are quoted as Scripture only by Latin-speaking writers, and only after the middle of the 5th century A.D.
3. Ancient translations: the disputed words are not found in any of the ancient translations of the NT made in the 2nd-10th centuries A.D.--Syriac, Coptic, Armenian, Georgian, Gothic, Ethiopic, Arabic, Slavic--except in Latin. The words are found in some manuscripts (but not the earliest) of the Old Latin version, and in many manuscripts of the Latin Vulgate (but not the earliest).
And for other pages on the matter you can try this Google search. Kiddpeat, recognizing someone may have through error or deliberate action introduced a passage into the bible during a time of heated debate over a particular subject is in the best interest of all Christians, whether it supports one's particular belief in a doctrine or not. I do not feel a need of an insertion to support the doctrine of a Trinity and as noted above, neither did the early church fathers.
I do not consider desiring the "sincere milk of the word" rather than implanted insertion of a false scripture (although the doctrine may be true) to be a vain and foolish matter. Quite the contrary I believe Paul was admonishing Timothy to use the entirety of scripture and the "gift" he'd received rather than allowing "fables" to become the standard upon which doctrinal beliefs were built.
The truth or error of the doctrine is not what was under consideration, but rather if the particular passage was true inspired scripture, or false.
Here I will put the verses, first with the insertion and then without.
I John 5: Who is he that overcometh the world, but he that believeth that Jesus is the Son of God? 6 This is he that came by water and blood, even Jesus Christ; not by water only, but by water and blood. And it is the Spirit that beareth witness, because the Spirit is truth. 7 For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. 8 And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.
I John 5: Who is he that overcometh the world, but he that believeth that Jesus is the Son of God? 6 This is he that came by water and blood, even Jesus Christ; not by water only, but by water and blood. And it is the Spirit that beareth witness, because the Spirit is truth. And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.
Most would agree, no matter what their belief in Trinity, that verse 7 seems out of context, interrupts the flow of thought which proceeds better without it and has that feeling of not belonging nor fitting the text. In fact, when you consider it, the verse doesn't even make much sense. Why would those 3 even NEED to bear record in Heaven and what does that have to do anyway with the theme of the chapter which is the witness of Christ to the world? The references don't fit the style of writing either. In all the rest of the chapter Jesus is referred to by name or as Son of God. ONLY in that one passage is he referred to as "Word". In all the rest of the chapter the term Spirit is used, but suddenly ONLY in that verse we see the term Holy Ghost inserted.
I believe those who are honest in themselves will realize the passage is some latter day insertion (for whatever reason) and recognize it not as true scripture.