In this chapter, the LORD explains how to make various signals on two silver trumpets, and then the tribes leave Sinai using the formation from Numbers 2.
This chapter continues with the military theme of Numbers by explaining the system of trumpet signals and the meanings therein. There are a few takeaways from this. It is interesting to note that trumpets have been used to signal various maneuvers in the battle field up through at least the American Civil War, though trumpets as a military tool have dropped off substantially since the advent of modern warfare, radios, etc.
In this chapter, we can see that the trumpets are being used for both military and non-military purposes, including both signalling in battle, as a triumphal note over sacrifices, and to help organize the camp. We already saw that the aptly named feast of trumpets (on the seventh month, first day) involves the blowing of trumpets. The Jubilee also requires the blowing of trumpets. In both these cases, it is celebratory.
The mixed role of trumpets is quintessentially Pentateuchal. I have already demonstrated that the text of the Pentateuch is extremely heterogeneous and drifts from history to law to poetry, etc, with seeming abandon. It is only appropriate, then, that their use of trumpets should be similarly heterogeneous. As a further point, this also highlights the ambiguity of the Israelite nation's identity as a whole. Since the trumpets are used for both military and non-military purposes, this shows that the intended recipients (the people) are considered both, possibly even at the same time. This ambiguity is reinforced by the language of Num 2 which talks about the tribal camps as being the "armies of" whatever tribe is mentioned. The tribe is the army and the army is the tribe.
The overall effect is that the Israelites are embarking on a total war. While total warfare is frequently considered a modern concept, as we can see it's really not. This is the first step for understanding why (in their later invasion of Canaan) the Israelites generally slaughtered women and children in addition to the men. I don't say this to justify the massacres, but so that my readers may understand the context of the decisions in the first place. There are other significant factors, such as the importance of stamping out the Canaanite religions, but just keep in mind that this is about survival for the Israelites and the Canaanites alike. More on this to come in Joshua.
Next we see the Israelites finally depart Sinai, when signaled by the cloud lifting off of the tabernacle. The departure of the tribes is virtually identical to the pattern laid out in Num 2, with two notable (but minor) exceptions. The first is that the Gershonites and Merarites carry the parts of the tabernacle after the first wave of tribes, while the Kohathites leave after the second wave (in the middle of the procession). Num 2 only said the Levites camp in the middle, and therefore would properly depart after the second wave. The explanation is pretty straightforward though: they wished to give the Levites time to set up the tabernacle before the holy things arrive into the camp.
The second exception is that the ark of the covenant traveled in the very front of the whole army (v. 33), which is the first time this has been mentioned. Of course we know from its position in the holy of holies that the ark of the covenant is extremely significant, but now we can see that it travels in the very front. Since the ark is considered like the LORD's throne (see e.g. Num 7:89), this positions the LORD at the front of the nation, like their king leading them into battle. This effect is deliberate, and this goes back to my long-running study of the various manifestations of God. Even though this isn't precisely a manifestation, the ark is symbolic of the LORD's presence and is positioned as the leader of the Israelite people. The cloud is a more direct manifestation and is also guiding the Israelites as they travel from campsite to campsite.
We also see the Israelites trying to talk Hobab (a relative of Moses) into traveling with them as their guide. He is reluctant, but after offering him implied wealth, he agrees. It is unclear what happens to Hobab after this, because he isn't mentioned again, except possibly in Judges 4:11 (which calls Hobab the father-in-law of Moses, but the father-in-law of Moses is Reuel AKA Jethro). Judges 4:11 seems to suggest that Hobab's family arrived in the promised land with the Israelites and settled there.
The last part of this chapter is a record of what Moses would say when the ark (leading the people) would set out or come to rest. Both of these phrases reinforce the association between the ark of the covenant and the LORD's presence.