Back in the ancient days, they passed their information on orally. It was the cuture back then. They didn’t have t.v., radio, video games, ect. They did alot more talking. They didn’t have access to pen and parchment as much either, so they passed along information orally. Their memories were much greater than our memories because they used them much more often. The bible was written down by the first hand witnessess within the lifetimes of them. It was completed by A.D. 90 by John who walked with Jesus. Jesus died on the cross around A.D. 30-33. So the latest book that was completed was around 60 years after the event by the eyewitness who actually KNEW Jesus Christ and saw His miracles, heard His words, ect.