Some of the sages state that this passage is (deliberately) out of place in the narrative, and the inverted Nun alludes that it should have been inserted some 50 (נ) verses earlier. In the Talmud (Shabbat 115b, 116a), however, it is stated that any part of the Torah with 85 or more letters is itself considered a "book," and therefore according to some of the Jewish sages this passage of Scripture actually demarcates a separate book of the Torah! If so, instead of the five books of Moses, we would have seven:
4. Numbers (1:1-10:34) [i.e., Numbers, Book 1]
5. Numbers (10:35-36) [i.e., Numbers, Book 2]
6. Numbers (10:37-ff) [i.e., Numbers, Book 3]
So what does this "book" of the Torah say? Well, before Moses would lead the Israelites to a new station in the wilderness, he would order the ark to be moved by the Levites and then would chant "Arise, O LORD, and let your enemies be scattered, and let those who hate you flee before you!" In Hebrew:
קוּמָה יהוה וְיָפֻצוּ איְבֶיךָ וְיָנֻסוּ מְשַׂנְאֶיךָ מִפָּנֶיךָ
ku·mah Adonai ve·ya·fu·tzu oy·ve·kha, ve·ya·nu·su me·san·ey·kha mi·pa·ne·kha
"Arise, O LORD, and let your enemies be scattered,
let those who hate you flee before you" (Num. 10:35)
When the Shechinah rested, Moses would stop the procession of the camp and chant, "Return, O LORD, to the ten thousand thousands of Israel." In Hebrew:
שׁוּבָה יהוה רִבְבוֹת אַלְפֵי יִשְׂרָאֵלָ
shu·vah Adonai ri·ve·vot al·fei yis·ra·el
"Return, O LORD, to the many thousands of Israel" (Num. 10:36)
This "book" was left unfinished, however, because of the "Sin of the Spies" (chet ha-meraglim) and the Exodus generation's loss of access to enter into the Promised Land. The "story" of what follows after Numbers 10:35-36 - namely, the outbreak of fiery judgment, the subsequent exile from the land, the various sins of the wilderness generation - was written as historical "sequel" instead. What should have been written is that the LORD (as symbolized by the presence of the ark) entered the land with the redeemed Israelites on account of their faith in His promises. Moses would have led the people directly to Zion! According to these sages, this part of the Torah is "yet to be written" and will be altered when the Messiah comes (i.e., returns).
Why don't the Nun's face each other? According to the Talmud (Yoma 54a), the two Nuns picture the two keruvim (cherubs) which hovered over the Ark of the Covenant. When the Jewish people pleased God, the cherubs would face one another; if, however, they were disobedient, these angelic creatures would turn away from one another in the direction of the Holy Temple. Sin causes a rip in the fabric of spiritual reality, causing the angels of God (symbols of the Divine Presence) to turn away....
From a Messianic perspective, it is fascinating to see that what immediately preceeds this "book" is the story of Yitro (Jethro), Moses' Gentile father-in-law, who was offered to partake of the blessings of Israel. This is a perhaps a picture of the so-called "Church age" - i.e., the time when God would offer His salvation to the nations of the world (as represented by Jethro) just before a time of purging of national Israel. In other words, we can read this parenthetical "book" as a time of special dispensation for the nations of the world to turn to the "Son of Life" and be saved.