from David Carr’s book on literacy and the creation of literature in the ancient world:
… many ancient texts were not written in such a way that they could be read easily by someone who did not already known them well. Indeed, classicists long ago noted that the oldest Greek manuscripts, written as they are all in capitals and without word separation or other marks, were constructed for reading by people who had already mastered the relevant text. It was only in the Hellenistic period, a time of broader education and increase in silent reading, that we first see the initial creation of some more reader-friendly teaching texts with word-separation and other helps, all in the context of early education. As we will see, most manuscripts in the Greek context were not designed to provide a first-time introduction to a given textual tradition but instead stood as a permanent reference point for an ongoing process of largely oral recitation. Though someone might have such a text before him or her in order to dictate to others or even perform part of the text, it would function more the way a musical score does for a musician who already knows the piece than like a book the reader has never encountered before. Certainly some masters of the tradition could sight-read such texts, but most—like many musicians—would have had to already know the tradition in order to be able to fluidly “read” it from the highly reader-unfriendly manuscript.
This kind of textual preknowledge is presupposed in other traditions as well. Most readers, not at the top of mastery of the Sumero-Akkadian cuneiform system, could not rapidly read a text without having a prior familiarity with it (or close parallels to it). Only then would the reader quickly know the value of a given sign in context. The hieratic writing system of ancient Egyptian texts likewise requires someone already highly knowledgeable about the given text in order to decipher rapidly the contents of a given passage. Even alphabetic systems like those found at Ugarit, Phoenicia, Syria, and Israel lacked vocalic marks that could aid rapid reading. One early manuscript for the Hebrew prophets does not even record the complete words of each verse. Instead, only the first word is given, along with the first letter of each succeeding word.
– David M. Carr, Writing on the Tablet of the Heart: Origins of Scripture and Literature, 4-5