“…And G-d spoke to Moshe in the Sinai Desert, in the second year of their exodus from the land of Egypt, in the first month, saying: Bnei Yisrael shall make the Pesach sacrifice in its appointed time…” – Bamidbar 9:1-2

וַיְדַבֵּר ה’ אֶל מֹשֶׁה בְמִדְבַּר סִינַי בַּשָּׁנָה הַשֵּׁנִית לְצֵאתָם מֵאֶרֶץ מִצְרַיִם בַּחֹדֶשׁ הָרִאשׁוֹן לֵאמֹר: וְיַעֲשׂוּ בְנֵי יִשְׂרָאֵל אֶת הַפָּסַח בְּמוֹעֲדוֹ – במדבר ט, א-ב

In Parshas Beha’aloscha, the Torah recounts how Bnei Yisrael offered a Pesach sacrifice in the desert. This took place in the month of Nissan, a month prior to events related nine chapters earlier at the start of the Book of Bamidbar. Rashi explains that the Torah does not document these events in chronological order, so as not to open the Book of Bamidbar with a source of shame for the Jewish people. For in the forty years that they were in the desert, this was the only Pesach offering that they brought.

But what was the shame in not offering the Pesach in the desert? Besides for the Pesach offered in Egypt, G-d commanded that the yearly Pesach offering be observed, “when you come into the land that G-d shall give to you” (Shemos 12:25). As Rashi explains, “The Torah makes this mitzvah contingent upon their entry into the land. In the desert, they were obligated to offer the Pesach only once, in the second year, and that was by explicit divine mandate.” If G-d had not commanded them to do so, why is their lack of Pesach offerings in the desert a source of shame? (See Tosfos, Kiddushin 37b)

The explanation is that unlike other mitzvos whose obligation is exclusive to the Land of Israel, the Pesach was indeed offered in the desert—upon explicit divine mandate. Hence, its fulfillment was not inherently contingent on arrival in the Land. Moreover, the Torah recounts how the insistence of a few individuals who were restricted from offering the Pesach (in the desert) brought about the mitzvah of Pesach Sheni, a replacement holiday for those who could not offer the first Pesach in its proper time.

Therein lies the shame in the Jewish people’s lack of Pesach offerings in their years in the desert. If G-d accepted the plea of but a few individuals who requested a chance to offer the Pesach, then He certainly would have granted an entire nation’s demand not to be deprived of this mitzvah. Knowing the possibility of offering a Pesach in the desert, how is it that for thirty-nine years no one requested that G-d grant an opportunity to observe this mitzvah? To hide this shameful fact, the Book of Bamidbar begins instead with the census of Bnei Yisrael, to demonstrate the Jewish people’s preciousness before G-d nonetheless.

—Likutei Sichos, vol. 23, pp. 65-70