The Jewish people were counted after the Chet Haegel, through half-shekels rather than by heads. One reason in the Pasuk why they used coins was so it could be a Kaparah for them, through the Zechus HaTzedakah. Another reason was to avoid the risk of plague that comes with counting individuals. Exploring ideas in Tzedakah, Ayin HaRah and Achdus Yisrael.