"Kol ish v'isha asher nadav libam osam l'havi l'kol ha'melacha asher tzivah Hashem b'yad Moshe, heivi'u Bnei Yisrael nedavah laHashem" (35:29)
The pasuk opens speaking of "kol ish v'isha" who wanted to donate to the Mishkan. It would seem to make sense for the pasuk to conclude "heivi'u... nedavah," meaning these same men and women mentioned at the start of the pasuk fulfilled their pledge and dontated. Why does the pasuk add the words "Bnei Yisrael" in place of "ish v'isha" as its subject?
My wife suggested that those who were true nedivim did not call attention to their gifts -- there was no big plaque, no dinner to celebrate their generosity, no announcement of their pledge -- nothing that called attention to the personality of the giver. These true selfless souls looked at their gifts not as their personal bequests, but simply part of the contributions of the people as a whole, hence, "hevi'u Bnei Yisrael..." (see Ksav Sofer as well)