Pesach Sheni, as compared to the other mitzvos of the Torah, is unique, in that the other mitzvos were initiated from above and given to Moshe Rabbeinu to “command the Jewish people . . .” — the mitzvos were not asked for.
As an exception to this is the mitzvah of Pesach Sheni, (one of the 613 mitzvos) which was given to the Jewish people only after they demanded of Moshe Rabbeinu “lama nigorah” “why should we be deprived” from making the korban Pesach, having been disqualified because they were tamei (ritually impure) or “far away”.
For someone to come and ask for a mitzvah is strange, when G-d nor Moshe doesn’t command it; Especially when we consider who were these disqualified individuals that demanded not to be deprived. The Sages explain that these people were involved in carrying the “bones of Yosef” (which were brought out of Mitzrayim) or that they were involved with Nadav and Avihu, the two sons of Aharon, who had expired in the mishkan. In any case, these disqualified individuals were not just ordinary people, but they had been chosen to serve in an elite group.
It follows that if all Jews had emunah (faith) in “G-d and Moshe His servant” how much more so, these individuals who were men of a higher caliber. Their emunah in Moshe was superior to that of all the Jews. Why then did they not have faith and depend on Moshe regarding the korban pesach: if it’s necessary for them to bring it then Moshe will tell them to, and if it is not necessary to bring the korban-Pesach, why push the issue?
We learn from Pesach-Sheni an amazing lesson: When a Jew feels that he is lacking and deficient in matters of yiras shomayim, Torah and mitzvos, he cannot rely on anyone, not on Moshe Rabbeinu not even (as it were) on G-d, and he doesn’t say “we have no one to depend on only on our Father in Heaven”, but he cries out “Why should we be deprived”!
In matters of “yiras shomayim” and “kedushah” you cannot depend on an initiative from Above, but one has to demand it on his own. Our Sages tell us (Berachos 33b) “all matters are in the hands of Heaven except matters concerning the fear of Heaven”.
Spiritual and heavenly matters are dependent on the freechoice of every individual. That's why G-d wants that one should demand his spiritual needs, and when one shows his yearning and craving for his spirituality, when one reaches out, his efforts are reciprocated, as we see with Pesach Sheni, that following the protest “why should we be deprived” — G-d gave them a new mitzvah of Pesach Sheni. But one must take the initiative. There is another lesson from Pesach Sheni being initiated by the Jewish people: There are those that complain, why is there constant talk about Moshiach’s coming?
“Ani maamin (I believe in the coming of Moshiach . . . I await his coming every day” — why is this needed, they ask, why can’t we rely on G-d that He will send Moshiach when He sees fit to redeem the Jewish people? In response to this question comes the lesson from Pesach Sheni: Although this mitzvah could have been given like all other 247 (positive) mitzvos, however G-d wanted to hear the protest and demand of the Jewish people who did not want to be deprived of this mitzvah.
This also applies to our demand for the coming of Moshiach! Not only is this not against Torah, G-d forbid, but on the contrary, the Torah commands us to demand the Geulah, as our Sages, the “Anshei knesess hagdolah” (Men of the Great Assembly) instituted the “shemonei esrei” prayer “Speedily cause the scion of Dovid Your servant to flourish . . for we hope for Your salvation every day”; “May our eyes behold your return to Zion in mercy” — and we are not content with this once a day but we persistently repeat this three times daily.
And by demanding the Geulah the Jewish people hasten the coming of Moshiach, that he come quicker than without the demand.
My Father-in-law, the Rebbe said about Pesach Sheni, that it is never too late. One can always rectify. Also if we previously did not focus on these lessons of Pesach-Sheni we can now take the inspiration, to focus our efforts to demand the coming of Moshiach, may he come immediately. (Pesach Sheni 5744)