How do we know that those handwritten copies weren't copied incorrectly to begin with?
Until you find a copy of the Pentateuch, for example, complete with a signature from Moses himself, verified by historians from all over the world, there is no good way to say that what we have is completely unadulterated.
The original Bible books were evidently written on material as fragile as that used by the Phoenicians, Egyptians, and Romans. Why, then, did the material contained in the Bible survive to become the world’s most published book? Professor James L. Kugel provides one reason. He says that the original writings were copied “many, many times even within the biblical period itself.”
How do modern translations of the Bible compare with ancient manuscripts? Professor Julio Trebolle Barrera, a member of the team of experts charged with studying and publishing the ancient manuscripts known as the Dead Sea Scrolls, says: “The transmission of the text of the Hebrew Bible is of extraordinary exactitude, without parallel in Greek and Latin classical literature.” Respected Bible scholar F. F. Bruce says: “The evidence for our New Testament writings is ever so much greater than the evidence for many writings of classical authors, the authenticity of which no one dreams of questioning.” He continues: “If the New Testament were a collection of secular writings, their authenticity would generally be regarded as beyond all doubt.”
“The transmission of the text of the Hebrew Bible [Old Testament] is of extraordinary exactitude, without parallel in Greek and Latin classical literature.”—Professor Julio Trebolle Barrera
Still in existence today are some 6,000 handwritten copies of the Hebrew Scriptures, or Old Testament, and some 5,000 copies of the Greek Scriptures, or New Testament
Hebrew scrolls were produced, and handwritten copies of them were made. As these copies wore out or succumbed to the effects of humidity or mold, they had to be replaced. This process of copying went on for centuries.
Despite the care taken by Bible copyists, some errors inevitably crept in. But did the copyists’ mistakes substantially change the Bible text? No. On the whole, these errors are insignificant and have no bearing on the Bible’s general integrity, as proved by critical comparison of ancient manuscripts.
“In the number of ancient MSS. [manuscripts] attesting a writing, and in the number of years that had elapsed between the original and the attesting MSS., the Bible enjoys a decided advantage over classical writings [those of Homer, Plato, and others]. . . . Altogether classical MSS. are but a handful compared with Biblical. No ancient book is so well attested as the Bible.”—The Bible From the Beginning (New York, 1929), P. Marion Simms, pp. 74, 76.
In the introduction to his seven volumes on The Chester Beatty Biblical Papyri, Sir Frederic Kenyon wrote: “The first and most important conclusion derived from the examination of them [the papyri] is the satisfactory one that they confirm the essential soundness of the existing texts. No striking or fundamental variation is shown either in the Old or the New Testament. There are no important omissions or additions of passages, and no variations which affect vital facts or doctrines. The variations of text affect minor matters, such as the order of words or the precise words used . . . But their essential importance is their confirmation, by evidence of an earlier date than was hitherto available, of the integrity of our existing texts.”—(London, 1933), p. 15.