Chapter 4 represents another census of the Levites, different than the one described in chapter 3. The previous census was executed to count the male Levites a month old and older and compare that to the number of first born males in all of Israel to see whether the number of Levites was sufficient to “cover” the first number of the born of Israel, to stand in for them in service to YHWH (there weren’t, so a redemption price was paid to make up the difference). This next census counts males between the ages of 30 and 50 for each of the three tribes of Levites. These would be the number of men eligible to do the work that is going to be laid out for each tribe of Levites in their service to YHWH (under the direction of the priests).
The Kohathites are responsible for the protection and transportation of the most holy things (think items that are used as part of the administration of offerings to YHWH). However, they still can’t touch them (you know, because they are holy things, and holy things can’t be interacted with common things, otherwise there are consequences). So, when the camp has to move, Aaron & sons must first go in and put all of the holy things away. The ark of the testimony is covered with the veil (that separates the holy of holies from everything else) and then that is covered with goatskin and THAT is covered with a cloth of all blue. Then they put the poles in it and Kohath et al can make away with it without the risk of coming into contact and dying directly.
Then the rest of the stuff. The table where the bread of the presence is held a blue cloth is added with all of the plates and incense bowls and such are added on top of that. Then a scarlet cloth and some goatskin. Poles in, good to go. Similar things happen for the lampstands, the altar (the leftover ashes get taken as well) and all of its utensils. All get bundled, covered in cloth and goatskin, and prepared by the priests so the Kohathites can transport them to the next camp. This all sounds heavy, and it certainly was, thus the count of only males 30-50.
Each Levite tribe and their work gets to be overseen by either Aaron or one of his sons. The Kohath tribe gets Aaron’s son, Eleazar. YHWH takes time to warn Aaron and Moses to protect Kohath and Co., ensuring that they aren’t destroyed. How do they do that? They pass on these instructions precisely and the priests make sure that all the stuff is wrapped well. Also, remind the Kohathites that if they peek, even for a second, it will be their last image before death.
Next, there’s a count of the Gershonites. The holy things being accounted for by Kohath, Gershon and sons are responsible for all the drapery. This means everything around the court of the meeting place as well as the curtains that covered the actual tent of meeting. If it’s a curtain, a descendant of Gershon is carrying it. The priests don’t have to pack any of this up, it’s not “holy” like the holy things the Kohathites deal with. The transportation and protection of the curtains fall under the direction of Ithamar, son of Aaron.
Finally, there’s a count of the Merarites, and they are responsible for what’s left: the poles, bars, pegs, and bases. Basically, these fellas carry the skeleton of the meeting place that all the curtains go on. They also fall under the direction of Ithamar, son of Aaron.
The chapter ends with an accounting of how many of these fellas fit the criteria for each tribe. All told, there’s 8,580 Levite males between 30 and 50 who will do this work to start, split between the three tribes. That’s a massive operation, but YHWH ensured there were enough fellas, clear responsibilities, and proper leadership in place so that His mobile residence among His people could be adequately transported from camp to camp.