Question: "How much of the Bible was transmitted by oral tradition?"
Answer: First, we have to distinguish between oral “tradition” and oral “transmission.” The term tradition implies a long-held belief or practice that is not necessarily connected to any explicit facts or evidence. Transmission is a method of conveying information. The content of the Bible was, in some cases, first relayed through oral “transmission,” but not as the result of “tradition.” Rather, what was being transmitted was a direct explanation of specific facts regarding certain people, places, and times. In most cases, the biblical text was put into written form at the time of, or soon after, the events described.
A good example of this is the book of Luke, which explicitly states its origins in chapter 1. Luke is putting the results of his investigation into writing, using the experiences of actual eyewitnesses. Historians have found Luke to be a first-rate source of accurate information. Parts of this Gospel could be considered “oral transmission” prior to his authorship, though many of the same facts are found in the earlier Gospel of Mark.
Mark is believed to have been written around AD 55, far too close to the events described for it to fall into the “oral tradition” category. Further, many people often forget that the Gospels are neither the earliest Christian writings nor the original sources of their contents. The letters of Paul, for example, were almost all written prior to the Gospels. In 1 Corinthians 15, Paul describes the basic outlines of Christian belief. He says these points are those he was taught at his conversion, which occurred just a few years after the resurrection.
The same can be said of the Old Testament. The words were being written intentionally, to record the message or events occurring. The Old Testament books are not collections of prior legends, phrased in “once upon a time” language, and they are not detached from historical facts.
This direct recording of messages and events is in strong contrast to the writings of other faiths, such as Islam. The Qur’an was carried exclusively in an oral form for the entire forty-year ministry of Muhammad. Small portions of the Qur’an were written in scraps and fragments, but never in manuscript form. Only after Muhammad’s death were his sayings put into a compilation, which was itself edited and revised until competing copies were destroyed by the caliph Uthman. Further, a major source of Islamic knowledge is the hadith, which are quite literally “oral traditions,” in that their only support is trust in the spiritual integrity of their sources. Islam’s process of determining this trustworthiness is known as isnad.
Another example of Christianity’s separation from oral “traditions” came from Jesus Himself. The Pharisees had used oral traditions as a means to interpret the Law of Moses. Although Jesus spoke highly of the Scriptures, He roundly condemned the reliance on oral tradition for its tendency to reflect the desires of the traditionalists, rather than the will of God (see Mark 7:6–9).
Oral transmission, in and of itself, is not a completely unreliable method, particularly for simpler messages. In a time when most people did not read or write, oral transmission was common, and maintaining the exact original words was considered critical. The real advantage of a written over an oral message is that the writing preserves a snapshot of a message from an instant in time. One can compare the differences between different claims objectively, and a single message can be re-read with identical precision over and over. According to internal and external evidence, the words of the Bible were preserved in written form extremely early as records of fact, not oral traditions.