Can the major contours of the portraits of Jesus in the New Testament Gospels be trusted? Many critics would argue not. The Jesus Seminar became the best-known collection of such critics during the 1990s as they alleged that only 18 percent of the sayings ascribed to Jesus and 16 percent of his deeds as found in the four canonical Gospels of Matthew, Mark, Luke and John, plus the apocryphal Gospel of Thomas, bore any close relationship to what he actually said and did. At the same time, a much more representative cross-section of scholars from about 1980 to the present has inaugurated what has come to be called the Third Quest of the Historical Jesus, in which a greater optimism is emerging about how much we can know, from the Gospels, read in light of other historical cultural developments of the day.
He goes on to reiterate a claim that has appeared previously in Evidence for God — that the sheer number of copies of manuscripts counts towards their accuracy, which simply (and obviously) isn't the case. If I have an unreliable document and photocopy it a hundred or even a thousand times, the reliability of that document remains unchanged.
Blomberg also mentions archeological evidence, but this was dealt with in the previous chapter and is similarly unconvincing — or irrelevant — as far as the supernatural claims of the Gospels are concerned. He then discusses the differences between the Gospel accounts, attempting to have his cake and eat it. Where they agree, the Gospels demonstrate their reliability. Where they disagree, that's entirely what he would expect, given their mode of transmission. On the one hand we have variations due to the vagaries of the oral tradition, on the other we have remarkable veracity due to the reliability of the oral tradition.
But first-century Judaism was an oral culture, steeped in the educational practice of memorization. Some rabbis had the entire Hebrew Scriptures (the Christian Old Testament) committed to memory. Memorizing and preserving intact the amount of information contained in one Gospel would not have been hard for someone raised in this kind of culture who valued the memories of Jesus' life and teaching as sacred.
Taking all the above into account, it would appear that the historical reliability of the Bible can be reliably assessed as "not reliable".