Editing Mesechtas Pesachim (section)

==== Pesach Sheni ====
There is a dispute in the Mesechtas whether Pesach Sheni (Second Pesach) is a holiday in its own right, or a make-up for the first holiday. According to the first opinion, that Pesach Sheni is actually a separate obligation for every Jew apart from the obligation of the first Pesach, the Rebbe explains that the action of making the (first) Pesach sacrifice remains in effect until Pesach Sheni. Therefore, even though Pesach Sheni is an obligation separate from the first Pesach, one who offered his Pesach sacrifice during the first Pesach is not obligated in Pesach Sheni, because the action of the sacrifice of the first Pesach remains in effect until Pesach Sheni.

These words are based on the approach of the Rogatchover, that a continuous action exempts a person from the mitzvah, on condition that at the time of performing it, the person was obligated.