On what grounds were the people concerned Tamei Nefesh?
What exactly, was their request?
Rashi: When Moshe told them that Kodshim cannot be brought be'Tum'ah, they asked why the blood could not be sprinkled be'Taharah, and allow them to eat it be'Tum'ah
According to the version of the Ra'am (Mizrachi)
Why did this episode have to come about for the Parshah of Pesach Sheini to come out? Why did Moshe not simply teach Yisrael about Pesach Sheini directly, like he did the rest of the Torah?
Rashi: The people concerned were Tzadikim, and, based on the principle 'One brings about merits via meritorious people, they merited to be responsible for the introduction of Pesach Sheini to K'lal Yisrael.
Why did the questioners add the word "be'Mo'ado"?
Seforno: They were asking to be permitted to eat the Pesach be'Tum'ah, since it was a passing Mitzvah whose time would expire the next day.