Ramban: For doubting their Rebbi's veracity (See Sanhedrin, 110a) and for negating the prophecy of a Navi.
3)
If "ha'Eidah ha'Zos refers to all of Yisrael, why did Hashem not add 've'E'eseh eschem le'Goy Gadol' ? like He said to Moshe after Yisrael worshipped the Eigel?
1.
Oznayim la'Torah: Because it is referring, not to all of Yisrael, but to the majority, who had gone to the entrance of the Ohel Mo'ed
1
to watch what hapenned to the two hundred and fifty men.
2