Reliability of the accounts of the New Testament, such as the Gospels, is tested through various methods:
Embarrassment: If a statement would cause embarrassment for the doctrine in light of the culture it was first practiced it, it is very reliable as reflecting original doctrine.
Dissimilarity: If a statement is very dissimilar from other doctrinal concepts of other theologies of the time period, it can be attributed, with high reliability, to its original source.
Multiple Attestations: Multiple records of certain events taking place, which are unlikely to have been influenced by one another in the writing process, are highly reliable.
Double Affirmation: Double affirmation, or the affirmation of concepts by opponents and proponents of Christianity during early years of Christianity’s birth, supports high reliability of argued doctrine.
Coherence: When a saying or deed of Jesus is virtually identical with a saying or deed that has already been shown to be most likely authentic to Jesus, the deed or saying under consideration can be attributed some reliability due to this.
Palestinian Jewish Setting: An aspect of the Jesus tradition is most likely authentic if it reflects the Palestinian Jewish setting of Jesus’ time accurately, by being appropriately reflective of the specific time and culture. The Gospels were likely written in a non-Jewish environment. If an aspect can be kept true with reference to culture and tradition, it can be attributed with some reliability as having originated from Jesus himself, in Palestine.