כי תשא את ראש בני ישראל ונתנו איש כופר נפשו…ולא יהיה בהם נגף (כי תשא ל: יב)

Because you will carry the Yidden, each man will give a ransom for his life (machatzis hashekel)…and there will be no harm to them.

The Gaon R’ Yitzchak from Volozin zt’’l traveled to Minsk to raise money for his Yeshiva by giving ‘drashas’ – insightful speeches.  A huge crowd came to shul to hear his drasha, and space was limited.  R’ Yitzchak exclaimed, “Rabbosai, now I understand the pasuk of “כי תשא..ולא יהיה בהם נגף” – how is the machatzis hashekel a protection against harm? Hashem said to Moshe “כי תשא את ראש בני ישראל”, he should count the Yidden, and he knew that there might be a lot of pushing since everyone wants to fulfill the mitzvah, and the pushing can be dangerous. Therefore, Hashem said, “ונתנו איש כופר נפשו” – they should know that everyone is obligated to give the money, if so, “ולא יהיה בהם נגף” – there won’t be any harm because if you know you anyways have to give money, then you don’t need to push.  

R’ Yitzchak told the crowd, “I want you to know that I didn’t come here just to give ‘drashas’, I came because of “מחצית השקל” – to collect money for my Yeshiva.”