In this chapters, Moses sings a song about the infidelity of the Israelite people towards God.
In my introduction to Deuteronomy I joked about a "song and dance routine". While I was being facetious, this chapter does actually have a song, and Deuteronomy really is a very heterogeneous source.
While I called this the conclusion to Deuteronomy, this part is really more like the Appendix. In my opinion, Deut 30 with the choice between good and evil is about the best conclusion to the covenantal text as you can get. The last four chapters (between 31-34) are more like miscellaneous things that the author wished to include at the end. This song is one of those things.
The song is somewhat related to the last chapter, because the previous chapter emphasized the future idolatry of Israel, and this song is similarly foreboding. The overall flow of the song goes like this: The LORD is great and he brought Israel out of "a desert land", and by the LORD's provision Israel ate food in the wilderness, "honey from the rock". In this case, "rock" is being used with dual meaning. It refers to both the dryness and emptiness of the wasteland that Israel inhabited, and is also a reference to the LORD, who is their rock as a stabilizing force and a source of strength, because it is a firm foundation and a stronghold for them.
This language should also remind us of the two rocks that Moses struck with his staff to bring forth water, though in the song Moses refers metaphorically to honey and oil coming from rocks (which does not occur in the Exodus or Numbers accounts of their journey).
Similarly, I think the wilderness referenced in this song should be understood as an implicit reference to the wilderness of Sin and the Arabian Peninsula, but also a metaphorical reference to the humility of Israel's origin as a nation, beginning with the 70 or 75 people who descended to Egypt from Canaan. We are to understand that in the immediate term, God was protecting Israel through their literal desert journey. But metaphorically, we should understand that the LORD watched over Israel when they were in Egypt as well and in the prior history of the patriarchs in Canaan.
Anyway, the song goes on to say that Israel grows fat on the LORD's provision and thus supplied, becomes arrogant and seeks other gods. We can possibly understand this as a historical reference to the golden calf from Ex 32, but I think it's much more likely that this is predictive of a later idolatry that was also referenced in Deut 31:16. The LORD responds by "making them jealous" with a hostile nation that the LORD will send to conquer them, breaking their pride with the ignominy of defeat. Deut 28:49 similarly predicts a hostile nation would invade Israel as part of the curses of disobedience, so this chapter is just poetically rephrasing the curse.
However, the LORD refuses to destroy Israel because of "the provocation by the enemy" who would rejoice over Israel's destruction. This is very similar to Moses's appeal in Ex 32:12, and just like that passage it shows God is interested in using Israel as an example to other nations, as an appeal for those nations to turn to him. If God were only interested in Israel, then the opinions of other nations wouldn't matter. But God intends to use Israel as a beacon to draw other people to himself.
Anyway, Moses continues by saying that the other nations have their own sins to deal with (v. 32-33, their wine is the venom of serpents), and because of the pride of these nations at destroying Israel, they will themselves be subjected to judgment by the LORD, who will bring about "vengeance" and "retribution" upon these nations (v. 35). In the end, the LORD will have compassion on his people, ridiculing their false gods a bit, but in the end bringing about restoration to Israel and devastation upon their enemies who have previously had victory over them.
This whole narrative is largely consistent with the threatened destruction and promised renewal in Deut 29 and 30 respectively. What's new about this chapter is that it includes a bit more information about how Israel fell into idolatry (through pride at her success) and also about the fate of the nations who punish Israel (that they too suffer destruction in the end, and for many of the same reasons as Israel).
I think an attentive reader could parse a bit more information out of the song by studying the specific appellations used, but I think my synopsis above captures most of the overall flow. We see God caring attentively for Israel, but then giving them over to destruction when they turn to other gods. We see Israel travel in a parabolic arc as they ascend from "the wilderness" into wealth and glory and pride, and thereby securing their own downfall back into famine and slavery, though with a promised restoration at the end. So I guess it's more sinusoidal than parabolic? (Ok, I promise no more math.) We see Israel's foes take a similar path as they rise up above Israel, crush it down, but through their own pride slip into their own destruction as well.
I think this is worth emphasizing because it is a very common biblical trope in the OT. It follows the pattern of Israel's history (though from Deuteronomy, it's still their future), and many of the prophetic writings contain texts very similar to what we see in this chapter, rebuking Israel for their wealth and pride and predicting (or sometimes recounting) the disasters that follow. Out of their disaster the Israelites sometimes turn back to the LORD and so the LORD brings about a restoration.
And that's Israel's history in a nutshell. They rise and fall in direct proportion to how much pride they have, which influences how much they seek the LORD. It is very cyclical. Through much of their history Israel has Moses-like figures who try to guide it to follow the LORD. These are the prophets. And then through much of their history they have kings, who sometimes lead Israel into good and sometimes lead it into evil. To read more on that, you will have to skip ahead to the "histories", the books of Samuel, Kings and Chronicles.
At the end of the chapter, the LORD tells Moses to go up a mountain and die already, but no, we are not done yet. The next chapter is Moses's "prophetic oracle", much like Jacob's prophetic oracle in Genesis 49.