According to a commentary on the Gospels that I have read, the first Gospel that was written was that of St. Mark, about 70 AD, and the last Gospel that was written was that of St. John, around 100 AD. So nothing was written for the early Christians (and for us) until at least some thirty-seven years after the death, resurrection, and ascension of Jesus. During these thirty-seven years, the teachings of Jesus were communicated orally by the apostles in their efforts to spread the good news as Jesus had commanded.
The first Christians appeared to believe that the second coming of Jesus would occur in their lifetime. However, they seem to gradually come to the realization that that was not the case. And so, under the guidance of the Holy Spirit, the four evangelists undertook the writing apparently to ensure that the oral traditions were not lost.
I am intrigued by two passages from the Gospel of St. John that seem to shed further light on the subject. The first comes from Chapter 20, Verse 30: “Now Jesus did many other signs in the presence of his disciples that are not written in this book.” The other is in Chapter 21, Verse 25: “There are also many other things that Jesus did, but if these were to be described individually, I do not think the whole world would contain the books that would be written.” The whole scene must have been so extraordinary. Imagine thousands of people (five-thousand at the miracle of the loaves and fish) following Jesus around the countryside - no cars, no horses, a few donkeys perhaps, but thousands of barefoot people on foot following Jesus down the dusty roads and watching as the countless miracles and healings unfold. There was no TV, no network news, no CNN ... only oral traditions being generated and shared.
Today, I’m thinking that the concept of “Sacred Tradition” should be considered here, as the Catholic Church teaches. In other words, the word of God comes to us through both Sacred Tradition and Sacred Scripture and not through Scripture alone (“Sola Scriptura"). For the first thirty-seven years, Sacred Tradition is all we had. Then, after all four Gospels were written, we have St. John telling us that there was a ton of other things that Jesus did that are not recorded in Scripture. To me, it’s not a stretch to say that there are many things that come from this large “volume” of Sacred Tradition that should be believed. I only wish I could have been one of the thousands. My shoeless feet probably wouldn't have lasted long on the dusty roads. But, hey, when the savior of all mankind is leading the pack and giving us the good news of salvation, who cares about their feet! Even the word "extraordinary" is woefully inadequate.