The first step in our investigation of Jesus is to obtain reliable sources of information about him. Somewhat surprisingly, there are many potential sources to assess; Jesus is incredibly well-attested compared to your average ancient teacher, especially considering that he didn’t write anything himself. Even when we clear away the sources that are historically unreliable (such as apocryphal Gospels) or too brief for our purposes (such as Tacitus’ single paragraph on Jesus), we’re still left with several lengthy sources about Jesus that have a good claim to historical reliability; these include the four canonical Gospels (Matthew, Mark, Luke, and John) as well as several of Paul’s letters, all of which are included in the Christian New Testament (abbreviated NT). Naturally, part of their claim to historicity is that these documents are quite old, dating back to the first or early second century. While we obviously want our sources to be close to the events they report, this desirable feature comes with a problem: if these documents had to endure 2000 years of history to make it to us, how do we know they made it intact?
Fortunately, this isn’t a unique problem – we don’t have the autographs (original copies) of practically any ancient work. What we do have are intermediate manuscripts, which are produced by copying the autograph or another copy. Textual critics use these manuscripts to reconstruct the original document as faithfully as possible; this process can be very involved, requiring knowledge of how the copying process for a particular manuscript was carried out, what kinds of errors were likely and unlikely to be produced in that manuscript, and so on. How well the textual critics are able to reconstruct the original text will depend on the quantity of manuscripts available to them and the reliability of the process by which those manuscripts were created.
In quantity of manuscripts, the New Testament is unparalleled. We have well over 24,000 manuscripts of the New Testament including over 5500 in Greek (the language in which the NT was originally written). Homer’s Iliad comes in second with nearly 2000 manuscripts while important ancient histories have a few hundred at most. (It’s also worth noting that the count of New Testament manuscripts does not include the over 1 million citations of the New Testament found in the writing of the early church fathers that help further establish the original text.) The abundance of New Testament manuscripts is obviously helpful in textual critics’ attempts to reconstruct the original documents, but strangely, it’s the reason for some of the most common popular objections to the transmission of the New Testament. These attacks, generally inspired by Dr. Bart Ehrman’s popular-level books on Biblical textual criticism, focus on the number of “variants” among NT manuscripts. As an example, consider Matthew 8:18, a sentence found in the New Testament Gospel of Matthew. In the English Standard Version, a typical English Bible translation, the verse reads “Now when Jesus saw a crowd around him, he gave orders to go over to the other side.” But there are 6 different readings of this verse among Greek manuscripts of the New Testament; where the ESV says “crowd,” manuscripts may say “multitude,” “multitudes,” “multitudes coming,” “vast multitudes,” “many,” or “many multitudes.” These different readings are called variants, and while the total number of variants is tricky to obtain, many estimates place the number at 400,000 or higher. (Skeptics will often note that this number is higher than the number of words in the New Testament.) But as the variants of Matthew 8:18 show, some variants simply don’t matter. In fact, the variants of Matthew 8:18 are more meaningful than the majority of New Testament variants, more than 80% of which are spelling errors or differences in word order that aren’t even translatable into English (since Greek word order is more flexible than that of English). The remaining variants are called “meaningful” because they actually affect translation, but within this category, it’s typically unambiguous which reading is the original (because, for instance, a variant may be found in just a single 9th century manuscript whereas one of its competitors is multiply attested by early and reliable manuscripts). Less than 1% of all NT variants are meaningful and have a viable chance at being the original reading of the text, and most of these are still so minor that they present virtually no obstacle to a historian attempting to learn about Jesus – remember, “meaningful” here means “translatable,” not something like “of great importance.” A partial list of NT variants can be found here; it doesn’t take more than a brief perusal of them to observe that they’re of pretty much no consequence to a historical investigation of Jesus, though of course I’d encourage everyone to investigate until they’re satisfied.
The New Testament also excels in the reliability of the processes that created its manuscripts. Christianity began as a movement within Judaism, and the Jews at this time had an incredible reverence for the Word of God. One of the manifestations of this reverence was the care with which they copied what Christians now call the Old Testament – they took great pains to avoid errors, utilizing a numbering system to double-check new scribal copies. The proof is in the pudding; comparing two extensive Old Testament manuscripts, the Dead Sea Scrolls (produced around the 2nd century BCE) and the Masoretic Texts (produced around the 9th century CE), we find that Jewish scribes were able to preserve the text to a remarkable degree. While many early New Testament manuscripts were not produced by scribes in the same way as these Old Testament manuscripts, the point is that these early Christian Jews were products of the same culture as those scribes and their immense respect for what they believed to be God’s Word would plausibly have led to similar care and concern for accuracy in New Testament textual transmission. Thus even for the interval between the composing of a New Testament document and the dating of its earliest extant manuscript, we have good “soft” evidence in our knowledge of Jewish copying practice that it wasn’t drastically changed due to copyist incompetence during that time.
But even if no errors were introduced by incompetence, how do we know that no errors were introduced deliberately? For instance, some very late manuscripts include an explicit reference to the Trinity in 1 John 5:7-8; this is known to be a copyist creation not grounded in the original text. It looks very much like a copyist, wishing that there were more direct Biblical proof texts for the doctrine of the Trinity, deliberately added one to the manuscript he was charged with producing. The reason we know that this was a copyist addition, though, is because it was just one copyist acting in isolation; the change that he concocted isn’t reflected in independent manuscripts. This is very likely how any deliberate edit to the New Testament would look due to the decentralized nature of early New Testament manuscript production. It wasn’t as though the church in Jerusalem had a factory churning out manuscripts and an accompanying master list of everyone who had manuscripts of a given book; rather, these documents spread organically through the early church across a wide geographic area with copies being made for individual churches by individual copyists as they were needed. One would have to postulate some kind of conspiracy to explain how a deliberate text alteration made it into a broad enough swath of independent manuscripts to be considered authentic by modern textual critics, and in addition to the general implausibility of conspiracies, it’s further implausible that a large enough number of copyists would have consented to deliberately changing what they believed to be God’s Word.
In conclusion, then, we have good reasons to believe that the New Testament has the same substance today that it had 2000 years ago. The abundance of manuscripts, though it creates many variants, allows us to easily judge which variant reading is authentic in the huge majority of meaningful cases; even in the very few cases where it’s tough to decide, very little is at stake from a historical point of view. And in the small interval where we lack manuscripts, we have good soft evidence that the documents weren’t substantially changed accidentally (because of Jewish care for God’s Word as demonstrated by their pristine preservation of the Old Testament during the same time period) or deliberately (because of the decentralized nature of early New Testament transmission). This doesn’t mean that the New Testament is historically reliable; works of fiction or totally fabricated history books could be perfectly transmitted after their writing and they’d still be terrible sources of historical fact. But having established that we have access to the substance of the original New Testament documents, we’re now in a position to assess whether they’re a good source of historical information about Jesus.