The history of writing may be broadly divided into two large periods: the instrumental and authoritative stages. In the first period, ranging from the invention of script to around 1100 AD in the West (yes, the West, as there is always a point of view from somewhere, and this is mine), writing was conceived as an extension of human memory, like an external hard drive set up to complement the internal memory bank. This was a period of human history dominated by orality. Some things were recorded for special commemoration, it’s true, but most of the memorising, storage (through socialisation, for example) and retrieval (through ritual performance, for instance), mobilised the human memory, both individual and collective.
The other period, stretching from the central Middle Ages to our present day, has been one where writing doesn’t play second fiddle to human memory any more, but has instead achieved a special status including, but not limited to, the power of adjudicating on an increasingly large number of social issues: epistemological (scientific, forensic, even religious knowledge), legal and, often, political matters. If before, roughly, 1100 AD, an oral eyewitness account could trump a written record in a court of law, this is far less likely to happen in a modern court. If Judaism, the Catholic and Eastern Orthodox Churches have absorbed orally transmitted wisdom (later coded into various texts, Talmudic, Mishnaic, patristic, etc), no orality as a source of divine knowledge was admitted in the constitution of the emergent protestant churches during the Reformation, which belongs to the ‘authoritative’ period of writing. This was, and continues to be, an age of ‘sola scriptura’ writ large (no pun intended). Luther’s slogan was not so much the rallying cry of a new faith than an acute insight into deep cultural change.
The authority of writing in the modern age is an indisputable fact. It led to the development of modern science, which cannot be conceived outside of script (just imagine a purely oral scientific community). The authority of legal writing (the written code, the written jurisprudential record) was one of the factors which helped establish writing as an objective reality and an unequivocal source of authority. Writing may originate in a subjective environment, but once it leaves its headspring, it acquires an objective existence and may be shared between individuals and groups. Writing doesn’t cease to be instrumental, like in the first stage outlined above, but it is no longer just an add-on. Quite the opposite, fewer of us rely on our own memory for storing information when we know that the information is available in written form. Thus, human memory becomes an add-on to writing, reversing the thousand-years-long evolution which led to the authoritative stage.