The Yalkut Shimoni questions the reason for atonement. What had Bnei Yisroel done that would have been considered sinful? Moshe was concerned that perhaps during the collecting for the Mishkan, undue pressure might have been applied upon people, causing them to contribute out of shame. This can be viewed as gezel, theft. Although a gift given under duress, out of embarrassment, is halachically valid, this gift cannot be considered b’ratzon, willful, as emanating from a total nedivus ha’lev, heartfelt contribution. In order for the kedushah, holiness, of the Mishkan to be pervasive, it was essential that it be built in total harmony with every person. Every Jew who contributed towards the Mishkan was requested to do so willingly.
Horav Aharon Kotler, z”l, infers from here that the kedushah of any mitzvah is dependent upon the element of ratzon and simchah, willingness and joy, inherent in it. If one is not excited and enthusiastic about performing a mitzvah, its kedushah is lacking. Indeed, accepting money from someone who contributes under duress is tantamount to accepting gezel. Rav Aharon explains that performing a mitzvah with simchah demonstrates the esteem one has for this mitzvah. Chazal tell us in the Talmud Shabbos 130a that any mitzvah which Klal Yisrael accepted with joy is still being performed with joy. The joy expressed in mitzvah observance indicates one’s appreciation for the value of this mitzvah. The excitement exuded for a mitzvah, the enthusiasm expended in its performance, shows how much one cares for the mitzvah. A mitzvah that is valued maintains the continued allegiance of its adherents, regardless of the pressures that might imperil its performance.