S'A Bardichev,
As you know, I OWE you a chassishe vort in honor of your madrega. I am copying it from the Gutnick Chumash. Enjoy it.
Pesach sheni, which is a compensation or correction for a prior shortcoming, represents the path of teshuva. Teshuva is unique in two respects:
a. Through observing the mitzvos, a person spiritually elevates and refines the physical world which he comes into contact with, but he is only able to elevate the permissible and not the forbidden. Through teshuva, however, even a person's intentional transgressions are tranformed to merits (Yoma 86b).
b. The spiritual effect of mitzvah observance on a person is cumulative. It thus takes many years of persistent effort and loyal adherence for a person to elevate himself to spiritual heights. On the other hand, teshuva is an instantaneous spiritual "leap" of quantum proportions, wherey a person can undergo a complete tranformation in just one moment. As the Talmud states, "There are those that acquire their portion in the next world in many years, and there are those that acquire in just one moment (Avoda Zarah 17a).
The above two qualities of teshuva are seen in the differences between the Second Pesach and the First:
a. Chametz represents the evil and the forbidden. Nevertheless, during the Second Pesach, "one may keep both chametz and matzah in the home" (Rashi to Bamidbar 9:10), alluding to the fact that teshuva can spiritually elevate a person's past forbidden acts.
b. The First Pesach spans an entire week, suggesting a gradual spiritual ascent through the course of time. The Second Pesach, however, lasts just one day, alluding to the power of teshuva to transform a person in a single instant.