(1) UNTO THE HEADS OF THE TRIBES. I believe that this section followed the war with Midian. The Midianite war therefore comes after it. Compare, And Miriam and Aaron spoke against Moses (Num. 12:1), which comes after and they abode in Hazeroth (Num. 11:35) as I explained. Scripture tells us that the children of Gad came to Moses and Eleazar and the princes of the congregation, and spoke their piece (Num. 32:2-6). Scripture then writes, So Moses gave charge concerning them to Eleazar the priest, and to Joshua the son of Nun, and to the heads of the fathers’ houses (Num. 32:28). The heads of the fathers’ houses refers to the already-mentioned princes (Num. 32:2). Moses told the children of Gad and the children of Reuben, and do that which hath proceeded out of your mouth (Num. 32:24). Scripture therefore reads, And Moses spoke unto the heads of the tribes. saying…(v. 2). When a man voweth a vow…he shall not break his word. Scripture there writes, he shall do according to all that proceedeth out of his mouth (v. 3).

(16) Then they stepped up to him and said, “We will build here sheepfolds for our flocks and towns for our children.

נבנה למקננו פה WE WILL BUILD [SHEEP FOLDS] FOR OUR CATTLE HERE — They paid more regard to their property than to their sons and daughters, because they mentioned their cattle before their children. Moses said to them, “Not so! Make the chief thing the chief thing and what is subordinate subordinate. First build cities for your little ones and afterwards enclosures for your flocks” (cf. v. 24) (Midrash Tanchuma, Matot 7).

Our verse may be understood when we consider what the Zohar volume 2 page 157 has to say about the purpose of the Israelites' trek through the desert. It was meant to enable the Israelites to seek out isolated sparks of sanctity and to release them from captivity. These "sparks" had been taken captive by the spiritually negative forces who have their home in the desert. G'd made the Israelites travel through such places in order that their sanctity would act as a magnet and attract such "lost" sparks of sanctity. The only way this could be accomplished was by means of total sanctity, i.e. a combination of the sanctity of Israel, the Presence of G'd, שכינה and the holy Torah. It required the presence of 600,000 souls which originated in holy domains. Moses matched these 600,000 individually holy souls, as he is perceived of as the tree from which all these souls are branches (compare Isaiah 63,11). In a combined effort these forces of sanctity were able to overcome the forces of impurity which kept many of these lost sparks of sanctity captive. According to the Zohar then these "sparks" could be captured while the Israelites were actively journeying not while they were passsively encamped, and it is this the Torah has in mind when writing "these are the journeys." The word אלה is indeed in sharp contrast to any other journeys ever described anywhere as never before had there been a journey which was accompanied by so many elements of sanctity.

(33) You shall not pollute the land in which you live; for blood pollutes the land, and the land can have no expiation for blood that is shed on it, except by the blood of the one who shed it.

“Take vengeance of the children of Israel on the Midianites and afterwards you will be gathered unto your people.” (Bamidbar, 31:2)
Midian teaches of illusion. Moshe was called the wisdom of all of Israel, as explained in Parshat Tetsave (under the passage beginning “Go command”). Here the Holy One, blessed be He is saying to Moshe that when the power of illusion (Midian) is removed from the heart of Israel, then the children of Israel will not need to use their wisdom in order to know God’s will. Then, even without thinking, their intentions will be according to God’s will.