And the Princes [heads of the tribes] brought the onyx stones, and the stones to be set for the ephod and the breastplate.” (35:27)
Rabbi Shlomo Yitzchaki quotes a Medrash, which elaborates: this is the totality of what they brought. The princes brought nothing else, because the rest of the nation — the “regular people” — brought everything necessary to build the entire Tabernacle (“And the work was sufficient for all the construction, in order to do it, and more” [36:7]). Nothing was left for the princes to give, save the stones for the breastplate!
The Medrash records: Rabbi Nosson said, why is it that the Princes gave first at the Dedication of the Tabernacle, whereas when it came to the actual construction, they did the opposite? The answer is that the Princes said: let the congregation give what they will give, and whatever remains, we will fill in. The nation then brought everything that was needed. This being the case, the princes said “what is left for us to do?” — and they brought the precious stones. And for this reason, they gave first when it came time to dedicate the Tabernacle. They didn’t want to make the same mistake twice.
Imagine a congregation building a new synagogue today. What would happen if a donor offered to “finish the job” after the other congregants had contributed whatever they wished? Obviously, the board would jump for joy. The synagogue would be built! And in fact, this would most likely inspire a more relaxed (i.e. lazy) attitude on the part of the fundraiser and the other congregants — after all, the money was as good as theirs already, due to the generous man or woman in the back. But according to the Medrash, it was the Princes who were guilty of laziness — and perhaps they underestimated the dedication of the people at large.
The Nation of Israel did not want to give up the opportunity to be part of the Temple. They didn’t hold back, and wait to see what others would do. Nor did they rely on the Princes’ guarantee. Each one said: I want to participate! It didn’t matter that the work would be done without them – on the contrary, no one wanted to be left out. Each one saw an opportunity to give, to contribute to the benefit of the entire Jewish nation, and did so. And they gave so much that there was extra. They gave so much that Moshe found it necessary to instructions out to the people to stop giving [36:6], assuring us that had he not done so, they wouldn’t have stopped for a good while longer.
The Chofetz Chaim of Radin notes that the Torah indicates the laziness of the Princes by dropping an optional letter “Yud” ordinarily found in the Hebrew word “Nesi’im,” Princes. By contrast, the Torah describes in full detail the gifts of each Prince at the Dedication of the Tabernacle — even though each of the twelve brought precisely the same gift as all the others. All of this, he explains, is to teach us the greatness before G-d of working together, with energy and dedication, rather than allowing feelings of superiority or jealousy to divide us. When people rush forward to work on behalf of the entire group — instead of holding themselves above others, or looking out for their personal interests — then this is valued dearly by G-d, the Torah… and by other people, as well. (Torah.org)