The first tool the scholars us is called ‘criterion of dissimilarity’. This says if something Jesus did or said clashed with the Jewish religion of his day (and therefore the religion of the first Christians) then it is more likely to be authentic. There are many examples of this. Indeed the whole gospel story can be seen as subversive to the existing Jewish religion. However, some specific examples would be Jesus talking alone to the woman at the well in Samaria, or the story of the Good Samaritan or Jesus and his disciples breaking the Sabbath rules, or Jesus sharing the hospitality of sinners or standing the Ten Commandments on their head with his Sermon on the Mount.
The ‘criterion of embarrassment’ says that if a saying or event was embarrassing to the memory of Jesus or the apostles it is more likely to be authentic. So Jesus losing his temper, clearing out the temple or calling a woman a ‘dog’ are all examples. The apostles being proud, vain and doubting is another. So the story of Jesus being baptized by John would be authentic because it shows Jesus to be subordinate to John. Other examples are the supposed illegitimacy of Jesus’ birth and the most obvious–his execution as a criminal.
The ‘criterion of multiple attestation’ says that “when two or more independent sources present similar or consistent accounts, it is more likely that the accounts are accurate reports of events or that they are reporting a tradition which pre-dates the sources themselves.” This is often used to note that the four gospels attest to most of the same events, but that Paul’s epistles often attest to these events as well, as do the writings of the early church, and to a limited degree non-Christian ancient writings.
The ‘criterion of cultural and historical congruency’ says that a source is less credible if the account contradicts known historical facts, or if it conflicts with cultural practices common in the period in question. Conversely, if the account matches up with the other known facts it is more likely to be authentic. So the gospel stories are evaluated to see if they match with the known historical facts, the geography, archeological findings, cultural customs and details etc.
It should be noted that the results of this method of textual analysis are not always unanimously in favor of the historicity of the gospels, however, the results are significantly satisfactory for professional historians and Biblical scholars working together to show that the gospels are, for the most part, historically reliable documents. Some scholars say that the historical parts have had mythological elements added to them through exaggeration or fabrication at a much later date.
However, one of the aspects of this analysis most often overlooked is the cross referencing between the epistles of St Paul and the gospels. Scholars are virtually unanimous in recognizing most of the epistles of St Paul to be written before his death in the Neronian persecutions in the year 65. While not personally an eye witness of Jesus’ ministry, the Book of Acts shows that he knew the other apostles and indeed, went to them for instruction and validation of his ministry. Most importantly, they are not written as gospels with the intention to glorify Jesus and make converts. They are letters to the early Christian communities scattered around the Roman Empire. They are therefore very accurate reflections of the people in those early communities and are accurate records of the beliefs of those early communities.
Concerning this creed, New Testament scholar, Campenhausen said, “This account meets all the demands of historical reliability that could possibly be made of such a text,” and A. M. Hunter wrote, “The passage therefore preserves uniquely early and verifiable testimony. It meets every reasonable demand of historical reliability.”
This is just one of about half a dozen such early creeds embedded in the writings of Paul. Here are some others: 1 John 4:2: “This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God”, “regarding his Son, who as to his human nature was a descendant of David, and who through the spirit of holiness was declared with power to be the Son of God by his resurrection from the dead: Jesus Christ our Lord.”, and 1 Timothy 3:16: “He appeared in a body, was vindicated by the Spirit, was seen by angels, was preached among the nations, was believed on in the world, was taken up in glory.”
What does it matter? What these early Christian creeds show is that the so-called mythological elements of the gospels (angels, resurrection, ascension into heaven, Son of God) were not much later additions and accretions to the tradition, but were part of the beliefs about Jesus from the very earliest days.