I like the way Karl put it down:
First of all, you approach the Bible as a book of history, nothing more. Then we check as to whether the earliest copies we have are accurate representations of the original writings. We know that many classical manuscripts we have from Greek and Roman authors are faithful to the originals, despite the fact that the originals, several hundred years older than the extant manuscripts have long disappeared. From the several ancient manuscripts of the Biblical books we have, we can tell from the consistency (with minor discrepancies) that what we have are faithful representations of the originals. Remember, the originals are long gone.
Now, while still looking at the manuscripts as mere history, we counter-check them against the beliefs of the ancient Christians, by referring to secular writings and extra-Biblical writings. The earliest Church Fathers wrote of their belief in Christ, and this is confirmed by secular writers, including the anti-Christian Tacitus. They write of believers who die for their faith in Christ. Now we look at what these writings tell of Jesus and we can draw only two conclusions: he was either what he said he was, God, otherwise, a madman. There is no middle ground. But the ancient martyrs died proclaiming with their dying breath, their faith in Resurrection of Jesus. Now people do not die for a hoax, if that is indeed what the Resurrection is. Neither do they die for a hoax. This is quite different from Muslim militants blowing themselves up for their own perceived gain; the Christian martyrs did not seek death, rather, they chose death rather than deny Christ and his Resurrection. From that we have to conclude that Jesus did indeed rise from the dead.
Now if Jesus did rise from the dead, then he had to be what he said he was: God. And if he was indeed God, then we have to believe the truth of what he said, and he said that he would establish a Church, which the gates of hell cannot prevail against. (Still, we look at the Bible as accurate history, not Scripture) and the authority to bind and loose.
And this Church with this authority bound the canon, declaring by divine guidance which books are indeed the inspired Word of God.