I interpreted it to mean that if we do not rely on writing, but merely use it as an augmentation, that our record will be incomplete and therefore not trustwort

I interpreted it to mean that if we do not rely on writing, but merely use it as an augmentation, that our record will be incomplete and therefore not trustworthy, just a list of rumors. To promote the writing to a first class witness is necessary for it to be truly a work partner, a reliable source and a type of a mind to confer and converse with, in a weird but equal way as another person.