The Written Torah isn't simply a means devised by the transmitter to encode information in written form. If it were, then once someone knows the information by heart, the writing no longer serves a purpose. Similarly, if one were to struggle for years and never retain anything, we would assume he wasted those years and writing is of no use to him.
The letters themselves are inherently spiritual, and awaken great spiritual power from the highest of places every time they are spoken or written, or even thought.
(paraphrased from Hesed L'Avraham 2:11)