From here we learn that the number of Bnei Yisrael is like the sand of the sea and should never be counted.
One could answer that the underlying concept behind the prohibition is that the Jewish People are a supernatural people and they are not limited in what they can achieve. Putting a number on someone or something is the ultimate form of limiting them; one is saying that this person or object is limited to a certain number or measurement, and cannot stretch to more than this figure. In contrast, the Jewish People are by nature supernatural and expand beyond any limits – so counting us (putting a number on us directly) would be defying our very existence as a supernatural people. Therefore, the Gemara is learning from the passuk in Hoshea that since we are a people without limitations, and this is reflected by the fact that our population numbers will increase supernaturally, it is forbidden to count us because doing so denies this supernatural character in attempting to bring us down to the finite expression of numbers and figures.
Haman was attempting to make the Jews a ‘natural advantage’ by offering a sum of money to Achashveirosh in exchange for the ‘privilege’ of exterminating the Jewish People. Haman was trying to declare the Jewish People a ‘sellable item’ whose value could be expressed with infinite money, thus denying their supernatural limitless (and valueless) nature.
The Jews are the only nation in the history of the world to have returned to its homeland three times. Similarly, although we occupy a mere 0.22% of the world’s population, there is no nation who has influenced world history to such an extent – monotheism, mass education, and even the basic premise of equal rights are some of the things which the world owes to the Jewish People. Further, we have survived miraculously as a nation despite widespread, irrational, obsessive, and almost constant persecution. The Sefat Emet puts this across beautifully, noting the irony in the fact that the night on which we recount the supernatural miracles that were performed for us during the Exodus is called ‘seder night’ (meaning ‘night of order’). The ‘natural order’ of the Jewish People, he remarked, is the supernatural order.
May we live up to our ‘natural’ abilities to break out of our limitations in achieving what we to have the potential to achieve.
Here we see that you are allowed to count Jews. You are not allowed, although Hashem gave three reasons why [WE THINK] he did this:
1) Out of love for His people, G‑d counted us at important points in our history. The completion of the Tabernacle was one of these occasions. 2) To ensure that the Jews had sufficient numbers to merit the dwelling of the Divine presence upon them. 3) To ascertain how many warriors the Jews would have in their upcoming battles to conquer Canaan.
Jews are in a state of unity, they are connected to their Source and do not need added protection. When they are counted as individuals, they become "separated" and are subject to individual "subdivisions".
Some say that King David certainly did not forget the prohibition, and he, too, counted the Jews indirectly; the problem was that he performed the count simply to satisfy his own curiosity, and not for a specific purpose. Counting Jews without a purpose is forbidden even if done indirectly.