Of course, something else commonly understood in my old church (and in my family after we moved away) was that the New Testament was founded on the Old Testament (also inerrant in its original form) and that it wouldn’t make much sense without that foundation. Throughout his ministry, Yeshuah (Jesus is the anglicized Greek version of his name) made constant references to the Old Testament, going so far as to say (in Matthew 5:18) that not so much as a yodh (the smallest Hebrew letter, which looked something like an apostrophe) nor a stroke of the pen (i.e. a serif on any of those Hebrew letters) of the Law (i.e. the Pentateuch) would ever perish before the very earth and sky (which the ancient heathens with their cyclical thinking believed to be eternal things) were destroyed. Self-proclaimed “Christians” who try to pretend the New Testament somehow nullifies the Old Testament’s teachings (as the heretical Marcion of Sinope infamously did) are therefore going directly against Christ’s teaching there; it’s rather contradictory to claim to be a Christian when going against the Christ for whom our faith is named.

The main problem with the Bible’s original form is getting at some of that context: as you say, the text we have is the bare bones of our faith. Faith also requires the muscles and flesh and blood of sacramental worship, practical application, and personal communion with our God. Still, those bare bones don’t lie—unless (like the “archaeoraptor” or “Piltdown Chicken” hoax) one puts them together wrong; which is one reason why my old church’s teachings on doctrine put a particular emphasis on 2 Timothy 2:15’s talk of proper handling or (particularly in the KJV and its derivatives) “rightly dividing” our Scriptures.

There’s also the problem of languages and the words they use being rather slippery items: so much so that God even threatened Israel in Deuteronomy 28:49 (and again in Jeremiah 5:15) with the punishment of being invaded by a nation speaking a language they wouldn’t be able to understand. The original manuscripts of the Old Testament are primarily in Hebrew and Aramaic, and yet by New Testament times, most Jews outside of Judea itself (and even many within it) were working from the Koine Greek translation known as the Septuagint. Aside from Koine Greek already being a rather lowly dialect of the language (nowhere near so orderly and sophisticated as the kind of Greek e.g. Socrates spoke in his time), the kind of Greek John uses in his Gospel and his three letters is so substandard that it could be considered a pidgin language, comparing to the standard Greek of his time roughly as Gullah compares to standard modern-day English.

Then there’s Luke, who (out of the four Gospel writers) was a native speaker of Greek and therefore the best at writing it. Ironically—however—he likely had to write his Evangelium and Acta originally in Latin, as he was writing to “Most Excellent” (Kratiste in Greek, Carissima in Latin) Theophilus; “Most Excellent” is how one addressed a man of Senatorial rank in Rome, something like how we address judges as “your Honor” in court these days. Hence, the Greek manuscripts we have of his writings were undoubtedly re-translated from his original Latin manuscripts (which the good Senator sponsoring his works had likely gotten copied in Rome so that it might be distributed to other churches throughout the Empire).

Of course, even within the same language, words have a way of changing their meanings over distance and time. For just one example, having “a gay old time” (as the old Flintstones cartoon theme song assured us we would) would mean something extremely different nowadays from what it did back in the 1960s; and what people in the UK refer to as “college” is what we describe as the junior and senior years of high school here in the USA.

Fortunately, due in good part to archaeology and to the historical records of our ancestors (fragmentary though many of them are), we do have considerable context to help understand the Bible in its original form. Courtesy of Tacitus, Suetonius, Dio Cassius, and Josephus (among others), we have detailed records of what was going on in Judea and the rest of the Roman Empire throughout Jesus’ and the Apostles’ ministries. Thanks in good part to what our archaeologists have dug up in Israel and throughout the Middle East, we also know a fair amount about what was going on throughout those Old Testament times. (Why was the prophet Jonah so determined to flee from his assignment of prophesying God’s words to Nineveh warning of its impending doom? Try reading some of the Assyrian Kings’ tablets full of their old war stories casually bragging of all the mass tortures and mutilations and slaughters they inflicted on their vanquished foes, and you’ll see why.)

Concerning Paul’s letter to the Laodiceans, I should point out that the passage referencing it (Colossians 4:16) actually refers to it as coming from the Laodiceans, though it was obviously his letter since he wanted the Colossians to exchange the letter he wrote to them for it. While the letter might have been one he wrote specifically to the Laodiceans, his instructions to exchange letters strongly imply that it was one of several such circular letters he had written with the intent that it be distributed to all churches. He wrote another such letter around this same time that we know today as his epistle to the Ephesians—although only because they were the first ones to receive it; a far likelier explanation of what that “letter from the Laodiceans” he mentions in that passage, therefore, is that it was one of the many copies of his letter the Ephesians had made and mailed off to the other churches and which had now reached Laodicea.

As for the importance of preaching in person, it’s true that in the Old and New Testaments alike, this made up the bulk of every man of God’s ministry; yet God saw fit to make these prophets (or sometimes their helpers, as with Jeremiah’s secretary Baruch in particular) write down what they were preaching for the benefit of future generations. Why else would we have the writings of the likes of Amos, Jonah, Daniel, Ezra, and Nehemiah, to name just a few? As in those earlier times, God continues to preserve those writings that tell us what we need to know: “blessed are those who have not seen, and yet believe” (John 20:29) and in the words of Matthew 26:11, “The poor you will always have with you, but you will not always have me.”

Speaking of what we need to know, and concerning the final words of John’s Gospel (21:10, which you cited), what he basically says there is “I could have written a lot more—we all could—but I think I’ve made my point.” A point the pastor at the church I’m currently attending brought up last year, and which I’ve also discussed with friends in a certain Bible study group is: how much Scripture does one truly have to know in order to be saved? For all the Bible’s complexities, salvation is not reserved only for scholars fluent in Hebrew and Aramaic and Greek and Latin who can understand all the nuances of any passage anywhere in the Bible well enough to explain it in depth and at length.

While the scholarly Jews who wrote the Talmud would probably love to bicker with each other endlessly over this question (and probably have; I haven’t read enough of that door-stopper of a volume to know), I do know that in the parable of the rich man and Lazarus, Jesus had Father Abraham telling the rich man in Hell that his five brothers still living could be spared his fate if only they would listen to and obey “Moses and the Prophets” (Luke 16:29-31) i.e. the Pentateuch and the histories in the Books of Samuel and Kings along with the “major” and “minor” prophets of the Old Testament—long before the first word of the New Testament was written and not even counting supplementary writings of the Old Testament like the Books of Chronicles or Job or Ecclesiastes and the like. Also, though the Jews listening to Jesus at the time did have a comparatively high literacy rate, a great many of them (possibly including that rich man and his brothers in the parable) were still illiterate and would therefore need someone else who was literate to read those Scriptures to them; hence the part about “listening” to them. Moreover, in the aforementioned Moses’ time, Israel had only that Pentateuch, and the vast majority of them were illiterate and needed someone to read it to them; and before that, Father Abraham himself had enough faith in God to get him into Heaven back when what would eventually be written down in Genesis was (probably) still an oral record.

All that said, I should also point out that in all these teachings from Jesus and the Apostles and their Old Testament predecessors, I’m not seeing any room for a sequel or any parallel writings. Part of the whole point of the Reformation was that Martin Luther (and John Calvin, and Ulrich Zwingli, among others) had noticed the ecclesial authorities of their time were interpolating and extrapolating an awful lot into the Gospel teachings that simply wasn’t there, e.g. where did Jesus or any of the Apostles ever speak of indulgences, or of “meriting the blood of Christ” or of Papal infallibility? Then, as now, the corrupt clergy (a great many of whom were shockingly ignorant of the very Scriptures they were supposed to be preaching) seemed to be very much like the Scribes and Pharisees Jesus condemned in Mark 7:6-7 for replacing God’s teachings with their own.

If anything, the Reformers were looking to strip away the dubious “supplementary” teachings the clergy had affixed to Jesus and his Apostles’ teachings like so many barnacles, not add to them. In many ways, the clergy had become like the many Gnostics and Judaizers and legalists in Paul’s time who had tried to roll Christianity up into some grander religious scheme with “deeper” learning and more elite ranking to be had: sure, basic Christianity is fine, but Christianity and [circumcision/a kosher diet/praying to Saints/Spiritualism/etc.] is even better! They were certainly not looking to write any new Scriptures.

Like those Reformers before me and like Paul and the other Apostles before them, therefore, color me skeptical whenever anyone comes proclaiming some new revelation is to be added to the Bible’s canon. Invariably, said “revelation” contradicts Scripture, usually quite brazenly and in a way obviously intended to trick Christians into accepting things like baby butchery, Climate Cultism, homosexuality, transer rubbish, polyamory, Liberation Theology, and religious syncretism into the church. (I’ve seen a church that fell prey to this kind of “revelation” in a town near where I live: it’s got a painting of one of those new epilepsy-inducing rainbow flags from the Alphabet Soup Nazis on a big granite edifice near its entrance and a sign reading “Everyone is welcome here!” to which I say “Everyone except God Himself… and any actual Christians, that is.”)

Long story short, while we can never truly understand all the finer details of everything in the Bible, it’s historically grounded, divinely inspired, has a proper ending (and John’s Book of Revelation, I should point out, is merely the capstone to numerous other prophecies and teachings about the End Times found elsewhere in both the Old and New Testaments), and plenty of instructions on what we are to be doing while we await that end. In short, yes it is sufficiently inerrant and complete. What teachings we have in the Bible are already far more than we need; and we do not need even more than that.