This is the Law of an Olah
It is noteworthy that after the Torah discusses the korban that a rich woman who has given birth brings, it says [Vayikra 12:7]: This is the law of a woman who gives birth to a male or to a female. The question is asked: Immediately following this verse, the Torah teaches us the korbanos that a poor woman who has given birth brings. Why would the Torah say regarding the rich woman’s korbanos that “this is law of a woman who gives birth”? It would seem from the verse that only the rich woman’s korbanos are the law, and not the korbanos from the poor woman.
The Kli Chemdah (Parshas Tazria) cites a Gemora in Menochos (110a): It is written: This is the law of an olah. The Gemora expounds: Anyone that studies the laws of an olah is considered as if he brought a korban olah. What would be if a poor person would recite the portion dealing with the rich person’s korbanos? Would it be regarded as if he brought the korban? The answer may be gleaned from the fact that the Torah concluded the portion dealing with the rich woman’s korbanos with the following verse: This is the law of a woman who gives birth. The Torah is informing us that the recital of this portion is sufficient for anyone, even for a poor woman.
[The Gemora states that Hashem told Avraham Avinu that whenever Klal Yisroel will read the Torah portions pertaining to the korbanos, it will be regarded as if they brought korbanos and their sins will be forgiven.
The commentators discuss if this concept applies by other mitzvos as well. Perhaps it can be said that the studying of any mitzvah that cannot be performed nowadays will be regarded as if one fulfilled the mitzvah.
The Chafetz Chaim cites the Gemora in Bava Metzia (114b) that the Amoraim were fluent in Seder Kodoshim in the same manner as Seder Moed, Nashim and Nezikin. This is because Kodoshim was relevant to them since the learning about the korbanos was regarded as if they actually brought a korban. Implicit in his words that for some reason this was only true regarding Seder Kodoshim and not to Seder Zeroim or Taharos which also has many halachos that do not apply outside of Eretz Yisroel and after the destruction of the Beis Hamikdosh.
The Taz in his sefer Divrei Dovid maintains that the concept applies to all mitzvos and one who studies the laws of Zeraim, it will be regarded as if he gave terumos and ma’asros to the kohanim and levi’im and it will be considered as if he gave all the presents to the poor people. This is the explanation in Yaakov’s words to Esav "Im Lavan garti," which Chazal understand to mean that Yaakov kept all 613 mitzvos in Lavan’s house. There were many mitzvos that he was not able to fulfill at that time; it is evident that the studying of these mitzvos are regarded as if he fulfilled them all.
The Ben Ish Cahi explains the verse in Nitzavim: "Ki Korov eilecha hadavar meod b’ficha u’vilvov’cha la’asoso." It is possible to fulfill all the mitzvos with your mouth (by studying them) even those mitzvos that you cannot actually perform.]
The Order of Serving Hashem
Our Gemora explains that a chatas should be sacrificed before an „olah but that the Torah put the verses of the „olah before those of the chatas because “for its reading, the Torah gave precedence to it”. Rashi (s.v. Lemikraah) comments: “that it should be read in the subject (of offerings) first” and Tosfos wonder (s.v. Lemikraah): “What kind of chidush is this?” HaGaon Rav Eliyahu Dessler zt”l writes that we can explain Rashi thus: In the order of sacrifices – i.e., in the practical phases of serving Hashem, the chatas – the rectification of sins – precedes the „olah – achieving high levels. But “for its reading” – i.e., to know and perceive high levels – “the Torah gave precedence to it” as even before the sinner finishes rectifying his sins, he should be familiar with all the levels. One cannot serve Hashem from a narrow viewpoint but one must be aware of all the stages of serving Hashem and the high levels that one must strive to achieve (Michtav MeEliyahu, III 174).