I'm basing all of my answer on this link here:
Chazal tell us in various agadot, that every letter of the Torah is important. They tell us in other agadot, that the Torah is written in the language of man, and thus we can presume, that not every letter of the Torah is imbued with special meaning. However, these two principles, though sometimes in conflict, should influence the way we read and study Torah.
So, when it appears obvious to us that a certain section of the Torah appears to be redundant, or 'useless' to the modern reader it is a good opportunity to pay closer attention to what is written in that section of the Torah.
Here, in regards to the census, is a careful analysis of the numbers.
While, I can not explain the significance of every detail to be learned, I will point out the areas of the text which should lead one to further study.
A few things stand out here.
- Most of the numbers are rounded off to the nearest 100, however in one tribe , the number is rounded off to 50 (gad in bamidbar), or 30 (Reuven in Pinchas). Where the numbers rounded off? Why?
- The numbers in the census, take a few months apart are exactly the same. How can this be? Didn't some people have a birthday?
- The numbers of First born males, within the population given of the census, and the number of Leviim given within the census, do not match up to logic. How could there be 1 first born for every 30 males?
- All of the summations of numbers are accurate, except for one. The Leviim. The Torah tells us there were 22,000 total, but doing the math by hand reveals 22,300 total. Why did the Torah give the wrong sum? Why does the Torah give us a total, when earlier it says not to count the Leviim?
- Why do the Levvim get counted differently than all the other tribes? And why is their number, despite having a larger range of ages to count, so much smaller?
- Why do most of the tribes keep the same number of people from census to census, but a few tribes, Shimon, Manesahe, and Ephraim to be exact, have such large differences?
Regardless of the details to the answers to all those questions, I would posit 3 things.
- The numbers in the Torah are not "trivial facts". In reality, they may not be "facts" at all. By comparing the Torah to logic and life as we know it, as well as comparing one part of the Torah to another part of the Torah, insights are derived. In addition, the Torah is not trying to give us pure historical facts, but rather is giving us a "general feeling" for what we need to know. Because of precision in one area, but not others, the Torah makes clear to us, that precision is not always the most important part of what we are being told.
- The Torah can not be understood, pasuk by pasuk. The Torah needs to be read and understood by looking at all parts of the Torah together. If you only read pasuk by pasuk, you will miss crucial lessons in the Torah. In this case, the crucial lesson seems to be, the non-precise nature of the numbers in what otherwise sounds like a "historical account"
- The Numbers the Torah provides us with are important, and not coincidence. Meaning, we can learn from the values themselves. If the Torah was being 100% accurate regarding the numbers, and was just giving us over pure, trivial facts, then we would not know to learn from these details. However, since the details are obviously not precise, we know, and perhaps are even forced, to learn insights from the specific numbers. Why 603,550/601,730 and not 600,00 as the Torah reports in Beshlach? (The Baal Haturim does a reverse gematria with the numbers, and says that the number tells us that each and every member of Israel, every single one of them, was counted in the census. "bene yisra'el kol rosh" ) Because of this, we can also ask, why are some tribes so much larger than others? What is the Torah trying to tell us?
The amount of Torah lessons we can gain from the Census, in multiple places in the Torah is immense, and to answer every lesson we gain would be beyond the scope of this question.