The Chasam Sofer writes that for this reason the Pesach Mitzrayim cannot be considered a korban. Furthermore, he adds, even the reference by the Gemara to the doorposts as a Mizbeach was only meant figuratively. The doorposts did not have the halachic status of a mizbeach, altar. 6 It should be added that korbanos may not be offered if there is no mizbeach.7

The Or Hachaim raises the following question: Why, when delineating the laws of Pesach Mitzrayim, does the Torah not mention that one who is tamei cannot participate in the Pesach ritual? It is only in the following year, in the midbar, that the Torah excludes those who were tamei from offering the Pesach. 8 The Or Hachaim responds one could not contract tuma before Matan Torah.

However, the Brisker Rav demonstrates from the following Gemara, that the Jews did indeed contract tuma before Matan Torah. The Sages debate the identity of the men who approached and complained to Moshe that they could not bring the Pesach because they were tamei. (We have the laws of Pesach Sheni because of them.) One opinion cited in the Gemara holds that they were the bearers of the Aron Yosef, Yosef's coffin. 9 Rashi writes that the bearers of the Aron Yosef placed the coffin down when they arrived at Har Sinai, before the giving of the Torah. Nonetheless, they were unable to bring the Pesach. 10

Given this Gemara, how then, do we answer the Or Hachaim's question: why was the Torah silent regarding the prohibition relating to one who is tamei participating in the Pesach ritual? The answer is that since - as we showed earlier - Pesach Mitzrayim was not halachically considered a korban, the restriction on tuma did not apply to it. Once the Mishkan was erected and they were commanded to offer the fats of the Pesach on the Mizbeach, a tamei nefesh became prohibited from participating in the Pesach.

Let us now examine the parsha of Pesach Sheni. The men who were tamei approached Moshe, saying: "We are impure... why should we lose out, by not offering the Korban Hashem?" 11 The difficulty is this: they knew that one who is tamei could not bring a Korban. Why then were they complaining? Were they insinuating that the halacha was unfair?

However, given our explanation that the first Pesach did not possess the halachic status of a korban, we better understand their complaint. The main mitzva of the Pesach is to eat its meat, as Pesach Mitzrayim demonstrates. Another illustration of this principle (from another halacha) is that although any individual who is tamei cannot offer a korban, if the majority of the nation is impure, or if a pure kohen is not available, then all the korbanos that are part of the daily, Shabbos, and festival services can be brought in a tuma-state. This maxim is known as tuma hutra b'tzibbur. 12

This leniency, however, only applies only to the avoda, the service of the Korban. Its blood may be sprinkled on the side of the Mizbeach, and the fats may be burnt on the altar's pyre. Nevertheless, it is forbidden for anyone impure to eat the meat of the offering. Despite the fact that there is a mitzva to eat from a Korban, since atonement can be attained without eating from the korban, it is therefore forbidden to do so. The Korban Pesach, however, is an exception to this rule. The very reason that it was brought was in order that it be eaten from.13

This was their argument! The men told Moshe that since the main mitzva of the first Pesach was to eat from it, eating the Pesach remains the main focus of the mitzva. That being the case, tuma should not invalidate one from participating in the Pesach offering, just as it did not in Mitzrayim. Although now they possessed the Mishkan, and they were therefore obligated to offer the Pesach on the Mizbeach, they nevertheless reasoned that the mitzva in essence remained the same. Hence they said to Moshe: Why should we be left out from offering the Korban Hashem? Why should we lose out on our mitzva, now that the Pesach is a korban that must be consumed on the Mizbeach for Hashem? 14

Footnotes

1. Shemos 12.
2. Bamidbar 9.
3. Ibid 9:7.
4. Pesachim 96a.
5. Rabbeinu Chananel; Aruch; see Rashi; cf. Meiri.
6. Chasam Sofer Yoreh Deah 235.
7. However, even with the presence of the mizbeach, korbanos are not permitted unconditionally. For example, when the Mizbeach stood, if the altar was damaged and rendered passul (invalid), any korban that was slaughtered beforehand, also became invalidated. (Zevachim 59a (see Avodas Menachem p229) In addition, these korbanos remained passul, even if the mizbeach was repaired on that very day. Furthermore, until the Mizbeach was fixed, it was forbidden to partake from any korban. Zevachim 60a See Tosafos ibid 61b and Bava Metzia 53b.
8. Or Hachaim, Bamidbar 19:2.
9. Sukka 25a-b with Rashi 25b sv v'im nosei arono.
10. Chiddushei HaGriz al Hatorah Bamidbar 9:6.
11. Bamidbar 9:7.
12. Yoma 6b.
13. Pesachim 62b
14. It should be noted that until these men approached Moshe, there is no mention in the Torah that one who is tamei cannot bring a Pesach. This was understood from the general rule that a korban cannot be brought b'tuma.
This also explains the ruling of the Tosefta Pesachim 8:7, that in Mitzrayim an animal with a cataract or similar blemish was not invalidated. For such a blemish only invalidates a Korban. Nevertheless if the animal was missing a limb, it would be invalid. See Yerushalmi Pesachim 9:5 cf Meshech Chachma, Shemos 12:5 s.v. seh tamim zachar.
See also Chasam Sofer ibid, for another difference between Pesach Mitzrayim and Pesach Doros.