If you do business of any kind you realize that contracts are a necessity (preferably a short, clear, one page contract if possible). The reason is to clarify expectations and intentions. We aim reduce risk. It also fortifies the agreement against the corrosive effects of time on the memory. Taken together these are the key reasons the Holy Spirit inspired the authorship of Mark and the other Gospels. True enough, human beings pressed the eyewitnesses to get it down on paper, but it was the Holy Spirit who guided the sacred process. Until then, oral tradition worked. But the world was rapidly changing. By the time Mark writes, thirty years had elapsed since the ascension. The eyewitnesses were getting old and dying off, or worse yet, being killed off during the early persecutions. Written words are necessary because oral tradition and human memory eventually fails. The verbal (word by word) inspiration of the Holy Spirit shepherds the process and guarantees we will know exactly what God himself wants us to know. He put it in writing. Proclaimers of that truth are obligated to preach it word for word if they intend to do justice to the story. May God help us.