The midrash (Shemot Rabbah, parshat Bo) exemplifies purity of faith, belief, and commitment in halachic life ("yehi libi tamim be-hukecha") by invoking two core mitzvot - korban Pesach and parah adumah. This unanticipated pairing is predicated on the fact that that each of these halachic pillars embodies the category of chok. The parallel between "zot chukat ha-Torah" (Bamidbar 19:2) and "zot chukat ha-Pesach" (Shemot 12:43) is noted to reinforce the link. [It is interesting to note that while the term "chok" is usually translated by Unkelas as "keyam", these two are rendered "gezeirat", signifying the formal category of "chok".] While parah adumah's credentials as the ultimate and personification of chok is self-evident, as it is defined by the paradox that effecting ritual purity triggers defilement of the purifying agent (metamei tehorim, metaher temeim), an enigma that even the wisest of all men was unable to decipher (see also Ramban Bamidbar 19:2), the characterization of korban Pesach as a chok, even as an archetypal chok, is more mystifying. The Torah does ubiquitously use the term chok in connection with the Pesach (see Shemot 12:14, 24, 43; 13:10, Bamidbar 9:3,12, 14). However, it also repeatedly provides a ready rationale - "u-pasahti aleichem" (Shemot 12:12, 13, 23, 27) for this unusual korban. This etymological explanation is frequently emphasized and is halachically consequential, as it forms the explication-recitation mandated by R. Gamliel (Pesachim 116b) in conjunction with the mitzvah of Pesach (See Rambam, Hilchos Hametz U'Matzah 8:4, Ramban, Milhamot, Berachot ch1, and his comments on hashmatat ha-esin no. 15) and the imperative of sipur yetziat Mitzrayim (Rambam, Hilchos Hametz U'Matzah 7:5), deepening the mystery of this uber-chok designation. Certainly, many of the specifics of this korban are singular, even relative to other korbonot, but these novel dimensions cohere compellingly with the evident motifs that underpin this mitzvah, reinforcing the impression of an accessible and rational mishpat, rather than inexplicable, impenetrable chok. Sefer ha-Chinuch (13,14,17 etc.) and Rambam (Moreh Nevuchim 3:53) supply additional perspectives that explore and accentuate singular facets of this challenging korban, reinforcing the enigma: in what sense is korban Pesach truly a chok, never mind one whose stature compares with or even equates to the uber-chok, parah adumah?
Numerous mefarshim engage the question of korban Pesach's chok status, even without the pressure of justifying this grandiose comparison to parah adumah. The Griz (also cited in Haggadah shel Pesach mi-Beit Levi) posits that korban Pesach is a chok to the extent that it belongs to the world of korbonot that generally attains that status. This approach is intriguing when one considers korban Pesach's extraordinarily distinctiveness within that world. While korban Pesach certainly retains the status of a korban (Rambam treats this topic in Sefer Korbonot, not in Avodah. See also Rambam Hil. Korban Pesach 1:3), it is offered outside of the "aleha hashleim" time frame of other korbonot (see Pesachim 59a and Rambam Hil. Temidim 1:4 and Lechem Mishneh), is developed in sefer Shemot rather than Vayikra, is designated as "Pesach la-Hashem", requiring lishmah in a manner that may exclude any obvious generic fallback status typical of most korbonot (see Zevachim 2a, Pesachim 61a and especially Rambam's view on Pesach le-sheim chulin - Pesulei ha-mukdashin 15:11), and it redefines, refines, or adapts many other korbonot conventions to project its singular message.
The Beit ha-Levi (parshat Bo) perceives the depiction of korban Pesach as a chok, despite the fact that the Torah provides a very compelling explanation, as exemplifying the perspective that all mitzvot and halachot are essentially Chukim, both regarding their ultimate Divine (and thus, unfathomable or impenetrable) purpose and with respect to the motivation of their execution. In a celebrated halachocentric passage, he argues that even halachic institutions apparently tied to historical events, like yetziat Mitzrayim, constitute transcendent themes that have independent value that may also be prior to or disconnected from the events that introduced them. [This halachocentric perspective coheres with, although it is a particularly striking manifestation of Brisker ideology.]
The Sheim Mishmuel (parshat Tzav - inyanei Pesach), specifically addressing the difficulty of this very midrash, emphasizes that it was vital that Benei Yisrael respond to this Divine imperative as if it was an unfathomable chok, or at least with no regard for its eminently evident objective. Consciously cultivating this submissive orientation was a critical step in the necessary transition from Egyptian servitude to enthusiastic immersion in Divine service and the exclusivity of Hashem's sovereignty. This process- the forceful substitution of Divine jurisdiction in place of dehumanizing human slavery- was a precondition to extricating the nation from the brink of spiritual extinction. Thus, the mentality of chok applied to the rational korban Pesach- "zot chukat ha-Pesach", constituted an important breakthrough in bringing about "halelu avdei Hashem- velo avdei Paroh" [This view is rooted in the insights of his father, the Avnei Nezer that are also developed in his halachic work (YD 554:12).]
Perhaps a brief reevaluation and expansion of the chok concept may further clarify the equation in the midrash between Pesach and parah adumah, the references to purity of faith ("tamim"), as well as the ubiquitous usage of "chok" in the korban Pesach context. While the paradoxical or unfathomable, exemplified by parah adumah, is the most ubiquitous and familiar chok, the concept is yet broader. The Talmud (Yoma 67b, see mefarshim Bamidbar 19:2 and beginning of parshat Behukotai) defines chok as something that is permanently etched in stone, and that should not be second-guessed ("chok chakti lecha ve-ein reshut le-harher acharei"). Unkelos typically renders "chok"-"keyama", an enduring law (though as noted, in these two contexts he opts for "gezerat"). The Torah often uses this term to express the enduring or permanent application of a law or laws, notwithstanding otherwise relevant changing circumstances. The laws are not only enduring, they are the core foundations for an unshakeable bond that itself cannot be intellectually rendered or even accurately articulated, but that is the sole anchor of a purposive life. Rambam, rightfully regarded as a colossal champion of religious intellectualism, unequivocally asserts (conclusion of Hil. Meilah) the axiological primacy of chukim over that of mishpatim, the more accessible rational mitzvot. This preference certainly reflects a profound awe and appreciation for the transcendent dimensions and the inner logic of halachic institutions and details. But it also spotlights the idealism and purity of motive and purpose that is entailed in and mandated by halachic commitment. chukim both test and further facilitate and manifest the permanent relationship with Hashem, which transcends pragmatic considerations as well as human understanding. Indeed, the midrash accentuates not subservience for its own sake, or even to initiate or reinforce submission, but pure and idealistic faith in Hashem- "yehi libi tamim bechukecha"- that extends to his mitzvot, and any Divine fiat. Parah adumah quintessentially embodies the most common application of chok - unqualified embrace of the intellectually impenetrable. Korban Pesach, though thoroughly comprehensible, constituted an act of faith in the most inhospitable of circumstances that absolutely defied personal self-interest and any pragmatic calculation. As such, it reflected the apex of chok-surrender, religious commitment, and faith that indelibly transformed Kelal Yisrael by cementing a permanent and unqualified bond with Hashem.
This bond was significantly formalized and advanced at keriyat Yam Suf, when faith and unqualified commitment was extended also to the role of Moshe Rabbeinu, the linchpin of the oral tradition and the embodiment of the halachic partnership between Hashem and Kelal Yisrael (Sheim mi-Shemuel, in his Haggadah, also develops this theme). It was then that "yehi libi tamim bechukecha" was converted into "vayaminu ba-Hashem u-be-Moshe avdo", triggering a spontaneous shirah that is an enduring expression of our spiritual aspirations.