According to Craig L. Blomberg’s Can We Still Believe the Bible?: An Evangelical Engagement with Contemporary Questions, perhaps more than you think. Reviewing the book, Louis Markos highlights areas where Blomberg pushes back against well-known critics of the Bible’s reliability, such as Bart Ehrman, arguing its trustworthiness “does not depend on its living up to logical positivist standards that would have meant nothing to Moses, David, Luke, or Paul”:
In chapter one, Blomberg puts Ehrman’s claim (from Misquoting Jesus) that “there are four hundred thousand textual variants among the ancient New Testament manuscripts” in the proper context. As he demonstrates, there are only two lengthy passages in the entire New Testament (the extended ending to Mark’s Gospel; the woman caught in adultery in John 8) that are sharply contested, and that do not appear in the oldest and best manuscripts. Neither of these passages contains vital theological or historical points that do not appear elsewhere in the Bible, and in all modern translations they are clearly marked as being questionable.
As for Ehrman’s 400,000 variants, Blomberg explains, they are “spread across more than 25,000 manuscripts in Greek or other ancient languages. … This is an average of only 16 variants per manuscript”. And of those variants, only “about a tenth of 1 percent . . . are interesting enough to make their way into footnotes in most English translations”. And the ones that do make it there offer no challenge to the authority of scripture on matters of faith and practice. “It cannot be emphasized strongly enough,” Blomberg concludes, “that no orthodox doctrine or ethical practice of Christianity depends solely on any disputed wording. There are always undisputed passages one can consult that teach the same truths”.
(An image of the Codex Sinaiticus, circa 350 A.D., containing the oldest complete copy of the New Testament, as well as most of the Greek Old Testament, known as the Septuagint, via Wikimedia Commons)