You're probably right in several ways. I would hope that the Christian community would be open to good scholarship regardless of how it coincided with their present understanding. Since Christians regard the NT record of Jesus' life as authoritative and inspired of God, they would naturally be reticent to accept an account that showed Jesus in a view that contradicted the Gospels. After all, we know there are many Gospels out there that give a totally fictional and spurious perspective on Jesus. No matter what it was, I doubt that it would be added to the canon. Christians believe that God has already made the decision of what would be part of the canon. But if the new discovery contained authentic and most likely true information about Jesus, I would hope it would be welcomed with open arms by both believers and detractors. To be responsible, we have to learn to accept what is shown to be true.

It's already been discussed what other types of documents have been found, so lets chat about how religious groups are likely to handle this. I predict the following basic pattern:

1. If it agreed mostly with their current view and didn't disagree in any major area, it would mostly have a neutral impact. Over time it might be added as Cannon, but also might not. That's really more of a political debate than a purely historical or theological debate.

2. If it disagreed strongly with their current view (but the facts supporting it as contemporary were not really debatable), the many groups would likely find another way to reject it (it was created to deceive perhaps). If it disagreed but the facts supporting it as contemporary were debatable, it would be rejected for that reason.

3. For any group not Christian, it would simply not matter much except perhaps to better clarify the Christian holy book.

There would be lots of variations of this by each group of Christians, but ultimately across all, it would likely have little impact because it would either be rejected (because it disagreed with the understanding today), or not matter much (because it didn't disagree in any important way)

4. For some groups, if it disagreed strongly they might go through the change required to adapt their beliefs to this new information and incorporate it going forward. But, I think 2 above is more likely for most groups, hence the low impact.

Like most respondents, I think an additional gospel would generally have a mild positive effect for Christianity, by providing more context. The canon of the Bible is not technically closed, but it would take an extremely persuasive book to make it into that rarefied atmosphere these days.

Specifically for #2, the name would make zero difference. Books were routinely attributed to people other than their authors (e.g. Gospel of Mary), or intentionally left as anonymous (e.g. Gospel of John), so the name on the tin doesn't mean much.

I think if we found something akin to the gospel according to Thomas Jefferson, where Jesus preaches his messages without any miraculous powers. (I don't mean to remove his claims of being the son of God and communicating with God, I mean without turning water into wine or walking on water, etc.) Something like that dating closer to Jesus' actual time would convince a lot of skeptics that at least 'historical Jesus' existed.

I don't think it would sway the faithful much to have another document. At best it may fix some disagreements between some congregations, and possibly unite more churches.

Well, if we just found another document that was basically like the Gospels, that would be less of a big deal. It would be one more of the many stories about Jesus produced around that time, and likely to be just as fabricated.

If we found a document that wasn't like a Gospel, but corroborated the Gospels using methodology suitable for critical historians of the era, that would be something. Heck, if we found a letter from a Roman visiting Jerusalem complaining about the streets being blocked by the throngs throwing palm fronds in front of this Jesus fellow, that would be better than a dozen new Gospel-style texts.

As others have said, for Christians it wouldn't really be a game-changer. There are other vaguely contemporaneous accounts and compelling scholarly testimony to other early documents (Q, etc), but the primary "canonizing" consideration for what constitutes scripture is that it was historically received and incorporated into worship. It might be interesting and shed light on historical events and practices after Christ's life, but since the scriptural texts themselves are understood not as a research endeavor but rather an authoritative record of those writings which were accepted and deemed worthy of preservation by the community. There's no historically-critical way of undercutting that or adding to it.
For me, if there were new documents which added to our understanding, as there have been (like the Dead Sea Scrolls), then that's all well and good, and historically interesting. If there are new documents which contradict the gospel accounts, even the source texts for those later accounts, (for example, a record of the sayings and teachings of Jesus without any references or claims to his divinity, the wet-dream of higher criticism), it wouldn't matter to me, because that text wasn't preserved and didn't enjoy perduring widespread use. As a Catholic, I don't believe in Christianity because the Bible furnishes evidence of events, I believe in the historical Church which defines and is defined by those texts it believes to have divine origin and to teach accurately what must be believed.

Good comments, and worth talking about. Matthew and John are the only ones would have claimed to have been eye-witnesses. Luke never claims he was, but self-admittedly composed his Gospel based on research. Mark is claimed by the Church Fathers to have gotten his information largely from Peter, so it's supposedly a second-hand "eyewitness" account.

That leaves Matthew and John. John, being the different Gospel, has many indicators throughout of being an eyewitness account. The argument that you've raised against Matthew is one of the strongest arguments against his authorship: An eyewitness wouldn't have to copy from another author, especially one who wasn't there (unless, of course, Mark's Gospel is really Peter's account, and Matthew knew the truth of it). It's very possible that there was a compendium of oral renditions of the life of Jesus being circulated, and all of the Gospel writers tapped into the same stories (since they were true) and they were the way people were used to hearing them. Some scholars have even speculated that Matthew was written before Mark, and therefore Mark was the copycat, but those scholars are by far in the minority.

And why were the accounts anonymous? There are three theories about that: (1) because it was the nature of the genre not to attach one's name, (2) because everyone knew who was writing them, and a name was unnecessary, or (3) because they didn't write them. Anonymity and interdependence doesn't necessarily require or imply that "they didn't know themselves," or that the accounts are false.

> That they are interdependent is no critique of their veracity.

It certainly can be, as I will demonstrate. At the very least it decreases their importance compared to independent accounts.
Why should a witness rely upon the testimony of another in constructing their own account of events? If an author was truly present then they should be able to provide their own view, and to not do so implies that they didn't know themselves. Why bother creating another account if they weren't going to provide their own view? If anything that would make "The Gospel According to..." bit an outright lie!

One anonymous account attributed to one person is bad enough, but one anonymous account attributed to several people is worse. An anonymous account with various creative edits traceable over time attributed to various people is downright terrible.

That is, if Q, J,E, D, or P are even real, which there is no evidence they are. No fragment or even mention of them has ever been found. It makes one wonder if it's all academic speculation without tie in to actual history.

Yeah, I think Q at least has a chance of being recovered, while it's a miracle that JEDP survived the Babylonian exile.

I agree that any new discoveries won't change any minds, but instead provide a better understanding of the hermeneutic history. I certainly don't believe any document from any time period could possibly make a difference in the mind of a skeptic. And I could say the same for the faithful.