This week's parshah begins with the mitzvah of machatzis hashekel. HaShem tells Moshe to count the Jewish people, but not to count them one by one. Instead, every one over the age of twenty had to bring a half-shekel. Then all the shekalim would be counted and in that way, Moshe would know the number of the people. Later, the money was used to purchase the animals offered as sacrifices.

But giving the half-shekalim was not just to figure out the number of the Jewish people. HaShem tells Moshe that the machatzis hashekel was kofer nefesh. Kofer is the root of the word kapporah. When we do kapporos on Erev Yom Kippur, we are telling HaShem that we are truly sorry for what we have done. We know that we ourselves should be punished for the things we did wrong. But we take a chicken instead and it is our kapporah - our atonement for our sins.

The half-shekel which the Jewish people were commanded to give was also like kapporos.

The pasuk says: "This is what they should give." The Midrash tells us that the word "this" teaches us that HaShem actually showed Moshe a half-shekel formed of fire and said: "Here, this is what I mean by a half-shekel."

The Midrash tells us that Moshe found it hard to understand the mitzvah of machatzis hashekel, so HaShem showed him the fiery coin.

We have other examples where Moshe Rabbeinu was shown things by HaShem so he would know exactly what HaShem meant. HaShem showed him the menorah, because it was a very complicated vessel to build. And HaShem showed him the shape of the moon as it appears on the night of Rosh Chodesh, so that the Jews would know how to fix the calendar.

But what's so hard to understand about a half-shekel? It's a simple coin. Couldn't Moshe Rabbeinu have known what a half-shekel looked like without HaShem showing him?

And if HaShem had to show him, why did He show him a fiery coin and not a regular one?

The answer is that surely Moshe Rabbeinu knew what a half-shekel was. But he could not understand how this coin, a small amount of money, could be kofer nefesh - an atonement for wrongdoing - even for such deeds that a person deserved to have his nefesh taken away.

So HaShem showed him a fiery coin. HaShem taught Moshe that when a Jew takes his money and gives it for a holy purpose - to bring the sacrifices, support Torah study, or help a needy person - and he gives it wholeheartedly with joy and eagerness, a simple coin becomes a coin of fire. Then that fiery enthusiasm connects the money to the fire he has in his neshamah. Giving the money for tzedakah now becomes so powerful that it can be kofer nefesh - an atonement for his sins.

(Adapted from Likkutei Sichos, Vol. II, pg. 677)