While many modern theologians shy away from using the bible as an authority for the existence of God, there still exists a strong number of theists out there who are willing to argue from the authority of the bible. Often the creationists will use that it's God's word in order to trump all discoveries by man, though that's not what I want to focus on today. Instead it's those who use the bible to assert that Jesus is God-incarnate. So much effort and apologetics is put into trying to show that the gospel accounts of Jesus are valid evidence.
The power of testimony
As astounding as it may seem, an inescapable part of the human condition is the transfer of information through anecdotes. It seems an affront to logic and reason but it's this very notion that allows for infomercials to be so successful. Withstanding proper scrutiny is not needed in order for the transmission of eyewitness testimonials, nor does it stop people from passing on information the same way. Whatever the cause of this trust and scepticism filtered through another's eyes, the effect is well seen. Humans are social creatures, and passing on information is vital to our survival.
So where does this go wrong? Alternative medicine is an obvious example, despite the inability of alternative medicine to show any progress in double blind studies it's still a multi-billion dollar industry. UFO abduction encounters are another, otherwise perfectly rational people are convinced they have been abducted. Those who talk to gods, almost without fail it's the a god they've been brought up to believe in. Communicating with the dead, psychic powers, horoscopes, claims of bigfoot, conspiracy theories, modern-day cults; the list could go on all day. All these concepts exist with almost no empirical evidence to support any of them, yet all those are passed on anecdote and a good amount of those are widely accepted as real phenomena by the general population.
In the middle ages, people were convinced of witchcraft. Small communities were rife with accusations and a fervor swept across much of Europe which left many were killed for being witches. In modern day Africa, this still happens. Yet would we take the eyewitness testimony of the Salem trials as being a confirmation of the truth that there is witchcraft? I would sincerely hope not, and hope the lesson taken is the dangers of accepting anecdotal information on face value.
The gospels traditionally have been regarded as accurate historical accounts of the life and divinity of Jesus. Yet the gospels are that same anecdotal storytelling that has been shown to have limitations. I've seen many try to push the gospels back to as close to Jesus as is possible, that they were written by the apostles who witnessed such events. We now know through investigation that it's not the case, that the gospels were written decades later by people who had never seen or met Jesus. But even if they were eyewitness accounts, as evidence it's still nothing more than anecdotal storytelling. Given the extraordinary nature of the claims, accepting that the miracles happened is putting credence into the storytelling.
Preceding the claim that the eyewitness testimonies of the Gospels are strong enough evidence for Jesus' divinity comes the notion of making sure there even is a historical Jesus in the first place. One simply cannot appeal to the gospels in order to establish that the gospels are correct that there is a Jesus, it's a circular position and thus outside sources that verify that there was a Jesus are needed in order to give at least some credibility to the notion. And there are some early historians who did mention that there was a Jesus. So there's at least some historical backing.
It's important to keep remembering that in any historical context that it's now advocated that Jesus was God-incarnate; that God came down to earth in human form only to be martyred and thus redeeming original sin. It seems absurd that the best evidence for God walking on earth is in the form of 2nd-hand eyewitness accounts and secular historians mentioning it in passing. Of course Jesus was not the only proclaimed messiah of the age, like today we see people claiming to be the second coming of Christ, back then messianic cults were common. And many of these cults had followers who claimed their messiah performed many of the ascribed miracles that are also part of the Jesus story.
There are supposed artifacts, most associated with the flagellation and subsequent murder. One hilarious artifact is the alleged foreskin of Christ. Yet there's not one, but several! Multiple chalices from the last supper, fragments of the cross, parts of the crown of thorns, the nails pierced through him, etc. Several of these items would be expected to have human DNA left on them, so firstly they could be verified against each other to show authenticity of stemming from the same source. Secondly they could be tested to show whether there's both male and female ancestry in them. Though this is somewhat of an absurd request, just a suggestion on how one can go about scientifically demonstrating Christ's existence and divinity.
There is selective bias when looking at history, finding relevant names and places then using those positive hits to confirm its validity while ignoring all the misses. For instance, in the case of Jesus asserting that it must have been true because Herod and Pilate were real historical characters. But there's no account of the slaughter of the innocent even by Herod's prominent critics, and the gospel of Luke puts the birth of Jesus 10 years after Herod died. Yet beyond these superficial glances at history, the biblical accounts cannot be verified or falsified as there is a distinct absence of evidence. In the case of God walking on earth, one would ponder why there wasn't a bigger deal made. Why important locations and artifacts haven't been passed down through the ages, or why many of the elements of the Jesus story bear striking similarities to other pagan deities.
The purpose of this was not to dismiss a historical figure at the start of Christianity, rather to demonstrate how appealing to the bible as evidence of Jesus' divinity is flawed. Eyewitness accounts and a couple of names in history should not be enough to convince any reasonable person of what is nothing short of extraordinary, that even if there were strong evidence that Jesus existed it would not demonstrate anything more than that Jesus existed. His divinity is another matter entirely and cannot be drawn from any text.