WCF 1.5 "... yet, notwithstanding [all other proofs and evidences separate or combined], our full persuasion and assurance of the infallible truth and divine authority thereof, is from the inward work of the Holy Spirit, bearing witness by and with the Word in our hearts."
The Word of God is self-attesting. There is no higher judge of its reliability than itself. That Word says, "My sheep hear my voice, and I know them, and they follow me:" Jn.10:27.
This is my opinion on the KJV discussion. This version is good, it might even be the best (though I'm not the judge of such things for the sake of others). Or, some other version might be the best in English; but vituperative arguments about it are a marvelous distraction that serves the Devil.
The text of Scripture is a medium that conveys the mind of God to men. Men's minds are receivers of that (special) and all other (natural) revelation. Take this illustration of our reception. Each version is like a radio, one GE model, one a Sanyo, one a Panasonic, one a RCA... pick your brand. One of these is probably "the best." Some people won't even listen to an "off-brand" radio--it offends their ears (so they say).
The transmission source hasn't changed. The environmental media (space/atmospheric conditions; physical bodies in the way) impacts the quality of the transmission: cosmic rays, sunspot activity, clouds, storms, heat/cold, etc. And finally, your listening experience: "Wait, did he say your or you're? experience or expedience?"
This is all quite analogous to our reception of the divine Word. God has spoken and his Word is as changeless as he is. Moreover, he is sovereign over that transmission, it's passage through time/space/human-hands, and its reception. He makes sure his intent gets through clearly to those who should have it, and that accurately.
But, he has allowed--to one degree or another, and for purposes which (again) men question or dispute--that the distance and effects upon his transmission on its way to us will be impacted by the effects of the universe. But, not so much as will sufficiently harm his elect people from taking a full benefit from what comes through to them.
To me--my opinion--arguments about the version we should use, if they rise to the level of wrath, are as helpful as arguing over who owns a better quality radio. It is my job, as a minister of the Word, to stand by one or many gathered to hear what comes out of the speaker and (like Philip) offer the true interpretation. I can do that with the KJV, or the NKJV, or the ESV, or some other.
I wouldn't do that with the JW's NewWordTranslation. Waste of time, the problem is the horrendous tuning of that radio. It was created to produce specific garbled tones and confuse the hearers. But it is ridiculous to claim that a similar motive stands behind standard translations other than the KJV. The worst someone can claim against them is--to return to the metaphor--that they were built to specs and calibrated on a band that (it is thought by some) drops the overall quality. But almost everyone agrees that the aim of standard translations is universal appeal and access and accuracy.
The fact that the radio analogy is presently tied to a "market share" construct, while deplorable in spiritual terms, only serves in my opinion to validate the illustration's usefulness in the modern context. Publishers and booksellers are trying to get market share for their version. Today there is little "ecclesiastical" control, or "state" control of some version--the latter of which is especially responsible (in the era of mass printing) for the ubiquity and lasting popularity of the KJV.
See, the concept of "version" is particularly dependent on the printing press. Without that invention, the Bible is still produced by hand, and continues to be subject to the limits of quality control under those conditions. Those conditions prevailed for 1500yrs (since Christ) and longer if the OT age is taken in separately. But no matter where the Bible existed, in what form, in what translation (and the translations were themselves subject to the same challenges) people who could access the Bible in a known tongue were able to gain sufficiently from that transmission, and medium, and offered interpretation, the knowledge of God necessary for their salvation.
There is not, nor ever has been, a humanly-produced "version" (whether of just one copy) so perfect an exemplar of the divine Word that not one letter (or syllable, or word) failed to come through flawlessly. The ear fails, the eye, the pen slips, the copy being copied is blurred on one word; all which could in theory be caught and corrected by some means of comparison etc. available at some cost. But a "static free" rendition is not to be had in a world of entropy and sin.
Yet, for all the likelihood of a natural "failure" of this transmission to get through accurately over +6000yrs, it has been Providentially preserved. There is nothing like it in the world. There is no substantive doubt of any part of the text, outside of a minor fraction of the overall presentation. And WHAT it says is in even less doubt than HOW it is stated.
If a man's doubt whether God has spoken arises because the static in his speaker (or the claim that just one speaker is "static free") caused him to question: "God wouldn't make a transmission that contains static, would he?;" we have seen the man's a priori, not a real challenge to what God might or might not do.
Would God allow someone to miss his intent (lacking a good ear or a reliable interpreter)? Would he allow someone to butcher his meaning? Would he allow failure to hear his transmission in some or any form? People who have a view of divine purpose that sees God either as "loving everyone the same," or as given to a kind of individualistic-ideal encounter that can't be misunderstood (think: if I read the Bible, it should be an experience akin to burning-bush clarity) have no room for God's real-world historical usage, no acceptance of the idea he might withhold his light for a time, to the loss of some men.
I do not doubt the Word has been "kept pure in all ages," (WCF 1.8). I also believe and preach every last word. I simply do not worry--and don't think anyone else should either--that this purity is only 99 & 44/100%, rather than 100%. Or that some men claim it is only 98% or 95% sure. <yawn> That seems like more than enough to believe on the Lord Jesus Christ, and order your steps aright.