And you should put into the ark the testimony which I shall give you. (Shemos 25:16)
Rashi seems to explain that the Torah is called a “testimony” because it testifies that Hashem commanded us to do the mitzvos.
This seems problematic. How can the Torah testify on itself?
The Orach Chayim explains that if the scribes of later generations will have a dispute as to the correct lettering in the Torah, there will be a sefer torah, which will serve as the standard, which will testify for the exact spelling and wording of the Torah. (similar to how the prototype meter bar is kept in Sèvres, France.)
Some people may look at the written Torah and feel that it is possible—albeit difficult—to observe it without the Oral tradition that normally accompanies it. However, Reb Michel Feinstein explains that it is totally impossible to keep the written Torah without the Oral tradition. If so, it would seem that the most important part of “the Torah” is the Oral law, and not the written law that is stored away in the aron. That physical Torah is there perhaps only to give us a basis for the Oral Law—but nothing more.
When I saw this idea, I was truly bothered because the halacha is that the written Torah must be placed on top of a mishnayos or a gemora. The reason for this is that the holiness inherent in the written Torah is of a higher caliber than that of the Oral Law (even when the latter is written), so it is seemingly more important.
I think the answer to this question is rather obvious. While at first it may seem that the Oral law is more important, because it is the key that unlocks the holy words of the written Torah. However, the written Torah is holier as it is the word of Hashem. It also testifies that there must be more than what is written. That which we are missing must come through the ‘less holy’ Oral law.
I think that this idea is found in the gemora in Chagigah, which says that people are foolish if they stand for a sefer Torah but do not stand up for a Talmid Chacham, for without the Talmid Chacham, the written Torah (on a practical level) is close to worthless. The Talmid Chacham enables us to function in the way the Torah wants, which is the essence of the service of Hashem and His Torah.