“Them” refers to the people, to those in charge of collecting funds. It definitely does not refer to Moshe Rabbeinu and Aharon HaKohen. They could not be the collectors, because If Moshe and Aharon were to come knocking on someone’s door and state that they were going door-to-door collecting money, would anyone be so audacious as to say, “no!”? Certainly not. One does not turn his back on the leaders of Klal Yisrael. This is not the way Hashem wanted the Mishkan to be built. It had to be the product of free-will contributions.
Furthermore, as Horav Reuven Karlinsky, zl, observes, if Moshe and Aharon were to collect the money through the medium of Ruach HaKodesh, Divine Inspiration, they would be able to ascertain and discern the origin of this money: Was it “kosher”? Was it earned appropriately, or through measures that are less than acceptable? If Moshe and Aharon were to canvass for appropriately-earned money, they might return with a paltry sum. They maintained extremely high standards, and few people would be able to live up to them.
The Satmar Rav, zl, was an extraordinary baal tzedakah. Once a young fellow studying in Kollel came to the Rebbe and asked for financial assistance. The Rebbe removed an envelope from his desk and gave it to the young man. Afterwards, a man walked in and, he, too, asked for assistance. The second supplicant was an ordinary man who had not been devoting his days and nights to Torah study. He was in need, and the Rebbe also gave him an envelope, but apparently the contents of the second envelope far-exceeded that of the first envelope. This prompted the first young man to return to the Rebbe and ask for a reason. (It is not that he was a mechutzaf, impertinent. He was not second-guessing the Rebbe; rather, he thought that he might be manifesting a personal failing which had prompted the Rebbe to diminish his portion.)
The Rebbe looked at the young man and asked, “You would like funds from that envelope? No problem. That money is readily available, and I will be happy to give you from there. The money that I gave you was from a special fund.” When the Rebbe saw that the young man was looking at him incredulously, he said, “Let me explain. I have a number of funds in my possession, monies that come from various sources. The money that I gave you comes from a source that is unusually blessed. How can you compare funds?”
People came to the Rebbe with money that they had derived from different sources and under varied circumstances. Furthermore, all of his donors were not alike. Some gave to impress, others out of guilt, while a select few gave what they had l’shem Shomayim, for the sake of Heaven. The Satmar Rav was a holy man who could distinguish between sources, and, as such, he made an effort to “unite” the benefactor with the appropriate beneficiary.