The fundamental question is whether the Bible is the insprired word of God or not. (It claims to be over 1500 times).
But putting that aside for a moment, let's look at one example. The dead sea scrolls contain a complete copy of Isaiah 53 written sometime in the 1st century BC. When compared to our copy today, there are 17 word differences. Sixteen of the seventeen are simply tense differences are other insignificant variations that have no effect on the text. The seventeenth is a translation of the word "light" that is different than today. However, the difference is immaterial to the context. Take a look at Isaiah 53. It is not short.
The second thing I would point out is that there are over 5000 extant copies from the 1st and 2nd centuries of the New Testament texts. By the time we reach the 4th century, there are 20,000. By comparing all the texts, Bible scholars are able to determine with amazing accuracy the original text. For example, if 19 of 20 copies contain the word "fish" in a particular passage and the 20th does not, we can conclude the 20th is a human transcription error. No other ancient document can even come close to the number of texts with which to work.
Further, the dates we are talking about in terms of ancient text analysis make the copies we have essentially contemporary to the original writing. Most non-Biblical ancient texts have only a handful of copies to work with that were written several hundred years after the original.
But we don't need to rely only on the text. By looking at the writings of early church fathers, we can reconstruct all but a few verses of the the New Testament through their quoting of it.
Some texts were rejected by early church fathers as not divinely inspired - for example the Gospel of Thomas. But if one looks at the rejected texts, what you will find is that they bare little resemblance to the accepted texts often containing fantastic elements and myth - for example, giant dragons and enormous crosses and the like.
Finally, if we look at the history of New Testament development, we find that by about 160AD we have a copy of the New Testament that is essentially what we use today (there were a view debates concerning a few of the books - for example, Jude and 3 John. However, the Gospels, Acts, Paul's letters and the other Apostle writings have always been considered scripture - even at the time they were written. Peter refers to one of Paul's letters as scripture and Paul refers to one of the Gospels as scripture (the greek word for scripture used by Peter and Paul appears 57 times in the New Testament - 55 of the 57 are references to the Old Testament, which was accepted to be divinely inspired. The other two are the two I mentioned.)
The bottom line is that we can trust the text we have today.
Thanks for that great exposition of the Gospels' legitimacy. I only wish that more people were aware of this simple truth. Unfortunately, the "people" love a good conspiracy and will swallow most anything.
Thomas is (purportedly) a collection of the sayings of Jesus, and contains no dragons or giant crosses or the like. Plus, given the difficulty of dating early Christian works, as discussed below, the provenance of Thomas is, for the moment, about as good as it is for any of the canonical gospels. One may debate whether it is divinely inspired or not, but the historical and archaeological evidence does not resolve that debate in and of itself.
Finally, if we look at the history of New Testament development, we find that by about 160AD we have a copy of the New Testament that is essentially what we use today....
There is no real support for such precise dating in the archaelogical and historical record, and such a contention is almost purely a matter of opinion, rather than of fact. The written gospels almost certainly predate the second century, but by how much, no one can really say with any certainty.