Where exactly, did they place the Sefer Torah that Moshe wrote?
Rashi: The Chachamim argue in Bava Basra, 14b, as to whether they fixed a board on to the outside of the Aron, on which they placed it, 1 or whether they placed it inside the Aron.
Da'as Zekenim, Rosh citing Ramban, both citing a Midrash: On Moshe's last day, he wrote 13 Sifrei Torah. 2 He gave one to each Shevet, and one was placed next to the Aron.
What is "ha'Sefer ha'Torah ha'Zeh" referring to?
Rashi #1 (citing R. Yehudah): Up to 34:4, excluding the last eight Pesukim. 1
Rashi #2 (citing R. Meir): Up to "le'Einei Kol Yisrael". 2
On what did the Sefer Torah testify?
Seforno: It testified that Hashem knew in advance that they would forsake His Torah, 1 and that it would corroborate everything that is written in the Sifrei Torah of Tzadikim of the generation - a proof that, word for word, that is what Hashem told Moshe at Sinai.
Seforno: Which explains why it needed to be placed in a location where nobody, other than the Kohen Gadol entered once a year.
