Lift up your heads, Oh charitable ones!

...Hashem showed Moshe a coin made of fire, a coin that was all quality and not quantity. Hashem's message to Moshe was that the half-shekel was not about showing off how much money one could give to charity. Rather, it was about each person making his contribution and showing that he counted in a meaningful manner. Each person's contribution was special, and when a person does something special, a person can be proud and can life his head up high. Thus, Hashem told Moshe to "lift up the heads" of the Jewish people. He commanded Moshe to teach the Jews a mitzva that would allow each person to feel pride in his role as an equal member of the Jewish nation.

http://www.chaburas.org/shekel.html