Do we have what they had? If Paul wrote under inspiration, is it conceivable that even one letter from any of his writings could be misplaced? This is the mistaken idea that lead to all sorts of objections to the Bible being the Word of God.
There are implications drawn from our not having anything short of a PDF of the original scrolls of the biblical books. Therefore I'll start with a discussion of the New Testament evidence and apply the logic of the conclusion to the Old Testament with only a brief overview of its manuscript tradition.
The Main Concern
I won't begin by citing that there are thousands of manuscripts (mss henceforth; singular: ms) of the New Testament (NT), compared to say 7 copies of Pliny the Younger's corpus, or that the earliest ms of Suetonius' Twelve Caesars (2nd century) is from the 10th century. These are important differences for some of our argumentation later, but as far as the central issue of "not having a letter dropped," they're irrelevant.
The idea is that any difference in our Bibles today from what any of the original authors had is a big problem. How could God's Word be different, or "flawed"? Isn't this supposed to be God's instruction of wisdom and way to salvation for all mankind?
The text and religiosity
This type of reasoning ignores something very important. Despite claims of inspiration (e.g. John 10:35), nowhere does the Bible insist that God's wisdom and way to salvation are encompassed within it if and only if it is 100% the way the original author wrote it, down to the very last question mark (which they didn't have). Imagine someone who's never heard of Christianity finds a Bible somewhere on the road. It's missing a few pages from the Pentateuch, maybe a few chapters from the books of Kings. Does this man receive any less of a message than if the missing history was there? Aren't Gideon Bibles shortened to only the Gospels and the Psalms? Does that make them mutilated and insufficient for preaching/missionary purposes? What about the early Christians who lived before any of the New Testament even existed? I get it now: Paul wasn't converted and saved on the road to Damascus; this happened only after he composed Philippians in Rome in the 60's AD.
This type of humanly biased mentality is exactly what many Muslim theologians throughout history have had about the Qur'an, leading them to believe and insist it has literally zero differences between today and the 7th century. I guess it doesn't count if someone rips a page from a Qur'an and sells it; maybe if he sold two such copies? At what point does this malicious salesmen refute the "inspired and unchanged" argument?
Misguided views on Infallibility
The point is that the idea that a book that God inspired men to write as a reflection and mirror of the conscience needs to be at all times 100% accurately transcribed is ridiculous. This is the origin behind the mentality of the King James Onlyist movement which considers the KJV completely errorless and an exact copy of the originals. And this type of reasoning in medieval Islam led to many of the theological schools concluding that the Qur'an was "uncreated". Since God's speech cannot be created at any point in time, and the Qur'an reflects it word for word literally, the book never really had an actual "origin"; only one that began on paper with Muhammad. After all, didn't Gabriel dictate God's words to Muhammad? In addition, this meant that God spoke Arabic! This in turn, led to the necessary idea that Arabic was a "divine" language. All the evidence for influence of foreign words from other languages was dealt with, for example, by saying that those languages copied Arabic. Where does it end with this kind of logic?
In fact, it was this very fallacious argument that made translating the Bible from the "holy languages" (Hebrew, Greek, and Latin - which no biblical author ever used) forbidden and a sacrilege up to only a few hundred years ago; something that Christians ironically get blamed for occasionally. Had anyone thought of such a wooden and fatalistic view of inspiration, the King James Bible translators would've never beautified it, particularly in its poetic sections such as the Psalms, with language that made it suitable for their era. Nor would have subsequent revisions (such as the one in 1769) been made for easier public reading.
This view isn't modern. Ancient Jewish scribes copying the Old Testament typically "updated" the language from the more archaic to the way it was spoken in their day. So, for example, the Isaiah scroll in the Dead Sea Scrolls has some small changes to read in later Hebrew. They continued doing this until around the 1st or 2nd century AD. [Siegfried H. Horn, "The Aramaic Problem of the Book of Daniel - 3" The Ministry Magazine Vol. 23, No. 3 (July, 1950), p.35] These changes are detectable, but minute enough. [ibid.]
The reason for this is exactly what we've been saying: God's message was not lost by these legalistic technicalities. The ancient rabbi Hillel was challenged by a Gentile to explain the whole Torah while he hopped on one leg, and Hillel told him exactly what Jesus says (Matt. 22:36-40) about the Greatest Commandment: "Love God and your neighbor; the rest is commentary." They didn't doubt or deny that Scripture was inspired by God, but God can infallibly tell you what you had for breakfast this morning: what's the relevance if it's just "commentary"? The Bible's main purpose was not an otherwise unknowable path to salvation, but a helpful guide in correct behavior. As Paul puts it, as examples for us (2 Tim. 3:16-17).
The teacher of the law in Matthew 22:34-40 tries to test Jesus by asking him which of God's commands is the greatest. This is a very good trick because if Jesus said, say, the first commandment - no other gods before me - then why is it that so much more of Moses' Law is devoted to the other types of offenses (murder, impurity, etc)? Surely God isn't this "egotistical" to think worship of Him is more important than preventing/punishing murder. Or if adultery is graver than theft, isn't it true that a man who has no money is in much more trouble than the one whose wife was unfaithful? How can any of God's commands be of "lesser" value than another. And this is why Jesus answers with what essentially boils down to a summary of the Law that the Old Testament itself gives, as well as an appeal to the conscience, just like Hillel; because there is no other "real" answer.
For example, the NIV notes that the word translated as "spearmen" in Acts 23:23 is actually "uncertain". There are numerous other examples, especially in the Old Testament (1 Sam. 15:9, 2 Kings 23:11, etc). Does it behoove the reader to know exactly what type of soldier Acts 23:23 has in mind? Are the identification of the birds mentioned in Deuteronomy 14:12, which the ESV says many of whom are unsure, so crucial to salvation? Oh the Israelites were allowed to eat bald eagles, but not bearded owls, we've been reading it wrong all this time, we're all going to Hell.
But I also want to show that despite this, the Bible has been textually preserved remarkably well; well enough for us to not even bother with the above argument.
Because of the thousands of mss and fragments we have a very good witness for the text of the New Testament and its variants from at least the 4th/5th centuries. The oft-cited figure of some ~98% similarity between the variants applies here, because this means we're still talking about the same Bible whose message is the salvation of the Messiah, Jesus Christ, and not a manual on how to successfully cultivate radishes in southern Italy.
The exact number ranges from 97.3% [a masterful assessment here] to 99.5% [Metzger]. I favor the lower range because of the evidence presented and the relative uncertainty because of what we don't know.
The Invisible first 200 Years
What we don't know is how accurately the texts were transcribed in the first two centuries after the NT was completed, namely 50-250 AD. This, however, wouldn't lower our "golden" 97% by much mostly because of Origen's Hexapla, which examined the different variants out of which came the Alexandrian family of manuscripts - the one used by most translations today. This negates the relevance of the claim, accurate as it would be, that we're blind to the earliest times of transmission for the NT, 50-250, and that copyist differences, be they harmonizations, doctrinal additions, or plain errors, are invisible to us; not to mention the poor quality of scribes that would've been available for the small, early Christian community.
The rate at which these differences emerged steadily declined as time went on. This is because of the exact same factors: more witnesses over a wider area and better scribes. These are simple spelling errors for the most part, and although even the omission of a single letter can sometimes change the meaning of an entire statement, this cannot change the general picture presented by the narratives in any meaningful way, as we noted above.
No Notable Difference in Divergent MSS Traditions
We have a few cases where the difference in some mss was bigger. The so-called "Western Text" of Acts, for example is 10% larger than our canonical one. Similarly, some of the DSS agree with the Septuagint text of Jeremiah, which is 1/7 shorter than the Masoretic. But this is nothing different from what we've discussed. If the consensus that the shorter version is closer to the original is correct, this changes no doctrine, especially since this is the version of Jeremiah in the Orthodox Church. The other way around is the same: it's the Western Bible's Jeremiah. The Western Acts is simply longer because of explanatory notes and the fact that we can detect it, and so much of it, which is also nothing different in substance from the Alexandrian text type, supports what we've been saying here, as well as the fact that Origen's Hexapla must've done its job. Moreover, the places where theology is most sensitive, the letters, has the least alteration mainly because of the non-historical nature which meant the scribe had fewer occasions to add explanatory notes - a feature reflected by the more "restrained" Western text of Paul's letters.
The situation with the Old Testament (OT) is exactly the same. Siegfried H. Horn cites Millar Burrows, an editor of the Isaiah Scroll from the Dead Sea Scrolls (DSS):
The most significant fact about the Isaiah manuscript is the degree to which it agrees with our traditional Hebrew text. The agreement is by no means exact in every detail. In the spelling of the words thare are a great many differences. Our manuscript was written long before the system of indicating vowels by points had been developed, and it makes very free use of the consonants (especially w and 31 but also h and aleph) to indicate vowels. In some cases the grammatical forms are different from those to which we are accustomed in our Hebrew Old Testament, especially in the verbs and the pronouns and suffixes. The grammarians will find considerable new material here for the historical grammar of the language. [Siegfried H. Horn, "The Aramaic Problem of the Book of Daniel - 3" The Ministry Magazine Vol. 23, No. 3 (July, 1950), p.36]
Horn's earlier summary and conclusion of the matter:
Although the differences are greater in other passages, the meaning of the text is nowhere changed. [ibid]
The same is true of the Loeb Classical Library's 1914 English translation of Suetonius' The Lives of the Twelve Caesars:
The translation of the Lives of the Caesars is based upon the text of Maximilian Ihm, Leipzig, 1907 (editio minor, 1909) with some slight changes in punctuation, capitalisation, and orthography, to conform more nearly with English and American usage. [Loeb Classical Library, Suetonius Vol I (1914), p.v]
The situation with OT mss transmission reliability is confirmed by small, specific values such as the reigns of the Hebrew kings which Thiele showed were accurate records of the length of their reigns; despite earlier assumptions of the exact opposite. [Thiele, Edwin R. The Mysterious Numbers of the Hebrew Kings (3rd ed. 1983), pp.208-209] There are some places where there was an obvious typo by, without a doubt, scribes, such as "Ahimelech son of Abiathar" (2 Sam. 8:17, 1 Chron. 18:16, 24:6). But again, these are trivial details.
The bottom line is that Origen's Hexapla, which was widely copied afterwards, would've mopped up many of the changes in the previous 150+ years. Paul's letters were certainly circulated as soon as he wrote them (Colossians 4:7), and were probably copied widely for Clement of Rome (c.96 AD) to quote Rom. 1:32 (1 Clem. 35) and 1 Clement 47 to not only cite 1 Corinthians, but to refer to Paul as having written under the inspiration of the Holy Spirit, only 40 years after its composition. Clement quotes and alludes to 1 Corinthians in several places, probably from memory as the allusions are about half, which shows that the Roman church must've had 1 Corinthians for some time for him to have read it and been very familiar with it. By 100 AD there was a sort of Pauline corpus of ten of his epistles (sans the Pastorals and Hebrews), which would've been unlikely if his letters weren't copied quite frequently. Marcion used these ten in his canon (c.150 AD). The Scillitan martyrs (c.180 AD) are said to have carried "letters of Paul" with them. The Gospels have a similar track record: Ignatius already cites Matthew in c.110 AD, and the famous Rylands fragment from John is already found in Egypt by 125 AD. Revelation (as well as 1 Peter) was well-known and liked in Christian circles by Papias' time (c.120 AD), and therefore must've also enjoyed a wide distribution, being apocalyptic literature which if accepted was typically popular most of the time in that era.
This widespread circulation makes it unlikely most of the errors/divergences from even the 1st century would've been undetected by the Hexapla. So for the vast majority of the text, what we can detect for the mss divergence from the 3rd century and on, Origen was able to do for us up to the early 3rd. And this is not including Patristic citations which are at the very least helpful with the context, if not the actual text.
Examples in Texts where Major and Minor Changes Matter
An example, not so much of minor errors changing the main meaning of a text, but of cultural misunderstanding is Pope Innocent IV's letter to the Mongol Khan Güyük asking for peace, which the Mongols understood as a desire for vassalage, as peace was a synonym to submission for them (similarly salam in Arabic and Muslim usage: peace and/or submission (islam) before God). Nevertheless, aside from this little contextual hiccup, the letters of Friar John to Güyük had to be translated from Latin to Russian to Persian to Mongol (James Chambers, The Devil's Horsemen, p.122), and the two groups understood each other on the technical level of language, so the telephone game is a very poor example of what supposedly happened to the Bible.
This is despite the fact that the Bible went through a much longer period of transmission: this means there were more copies to correctly preserve the text, as more copies would mean fewer credibility for divergent readings, and this is what we see. Since the low amount of copying is precisely what makes the first 100 years of the NT text invisible to us, the argument with the letter to the Mongols here applies at least in the basics.
The situation is very different with historical texts where we're concerned with minor details. So, for example, the famous lacuna in the Nabonidus Cylinder as to who Cyrus attacked and conquered in 547 BC (most likely Lydia - Urartu) makes a difference for us. Because we are dealing with relevant minutae.
Similarly, different mss traditions of Caesar's Civil Wars would matter for these reasons. Hence why the translator of the 1914 Loeb Classical Library edition, A. G. Peskett writes:
Anything in the way of commentary on the subject-matter is excluded by the scope of the Loeb Library, and I have only added a few explanatory notes here and there, though there is scarcely a chapter in the book that does not give occasion for lengthy comment in the sphere of political or military history, antiquities, and topography. My own Pitt Press edition of the Third Book (1900) contains one hundred pages of notes, few of which, I think, are wholly superfluous. The reader, if he wishes for a thorough understanding of Caesar's narrative, should have for reference some comprehensive history of Rome, such as Mommsen...a good recent manual of antiquities...[Loeb Classical Library, Caesar: The Civil Wars (1914), pp.ix-x]
For the constitutional questions involved in Caesar's candidature for the Consulship the student should consult Mommsen, Die Rechtsfrage zwischen Caesar und dem Senat, and Nissen, Uber den Ausbruch des Bürgerkrieges, to mention only two among the numerous books, pamphlets, or articles in periodicals, British or foreign, dealing with the constitutional history of the period. [ibid., p.x]
How does this, along with the countless Talmudic rules and regulations, compare with the Greatest Commandment to simply love God and your neighbor? Jesus wasn't kidding when he said he'd come with a light burden and to take off the yoke (Matt. 11:28-30).
It's clear that insofar as the New Testament message of "believing God raised Jesus from the dead with your heart" (Rom. 10:9) is concerned, the Bible does not detail with such needs for extensive explanatory materials. These are used only to better understand the biblical world, sometimes for the clarification of advice, sometimes for interest's sake; and for the apologist to answer intellectual attacks.