The difference between written Torah and oral Torah is that written Torah is ALL THERE AT ONCE, while Torah transmitted orally is given over piecemeal, little by little, detail by detail and only at the end everything comes together to form a cohesive whole.
Rav Chaim Volozhiner used to say that the difference between his brother R' Zelma'le and his Rebbi the Vilna Gaon, was that his brother knew the Torah like a Jews know "Ashrei" but only forwards from beginning to end. The Vilna Gaon knew Torah forwards AND backwards equally. The Brisker Rov explained that that there is דין of כתבם על לוח לבך [Mishlei 3-3] which means that the Torah must be written on a person heart as it is on a board. When it is written before a person, it can be read forwards and backwards equally. The Torah should ideally be perceived by a person in the form of the written word.
This is also the difference between seeing and hearing. When you see something it is always as a whole. You what in the foreground is together with what is in the background. That is comparable to כתב - the written word which is all there at once. Hearing is only received detail by detail, point by point. You hear one sound, combined with another few sounds which you [MIRACULOUSLY] combine in your mind to form a word which you instantaneously identify and translate into what you understand these sounds=word mean. Then another word which you first once again combine the sounds in your mind to form a word you can identify. Then you combine the second word with the first word and are able [again, miraculously - we just take it for granted] make meaning from these two words in sequence. Then a third word, a sentence, a paragraph, an entire lecture. Your mind combines all the sounds together to form perceptible meaning. It is impossible to hear everything at once. But we do see everything at one.
Seeing is the vehicle to understand writing. Listening is the vehicle to understand speech. That is the nature of תורה שבכתב and תורה שבעל פה. Torah Shebial Peh is the step by step understanding. Torah Shebichtav is where everything is there in toto. [If one letter is missing the entire sefer Torah is pasul. That is because כתב must be a שלימות. The same law doesn't apply to תורה שבעל פה where there are many many separate details that WE must connect with our שכל].
Our seeing today and our perception of תורה שבכתב is really "Shmiya-dik" and Torah Shebial Peh-dik. The writing per se has a שלימות but our perception is limited to the details. THAT is the root of all sin - ראייה חלקית. Seeing only partially when you think you have the whole picture. ותרא האשה - Chava saw but it was only part of the picture and that is what led to the sin.
Much more here.
