Because each mitzvah that you do is so important and special, sometimes Hashem will rearrange nature just for you.

This is evident in the story of when the Jewish people retrieved the spoils of the war with Midyan. Hashem commanded an accounting of all the spoils, which came to 840,000 animals, and then to split them. Half should go to the Warriors-half the Jewish people- and then take taxes from each half -each within each category. The Torah keeps repeating the exact numbers again and again. This was an extremely time consuming accounting; splitting and taking off the tax. Hashem made sure that not even one animal should die, in order to have the exact number to be able to do the mitzvah precisely. In other words, for years in advance, Hashem assured that they didn’t buy too much or too little cattle; that there were not too many births or deaths, so that one day when the Jewish people would be granted the spoils, that they should be able to fulfill the mitzvah correctly and accurately.

לקו״ש י״ג-ב