Commentary for Leviticus 12:8

אחד לעלה ואחד לחטאת THE ONE FOR A BURNT-OFFERING AND THE OTHER FOR A SIN-OFFERING — Scripture puts it (the עולה) first only by way of mention, but so far as offering it is concerned the sin-offering precedes the burnt-offering; thus do we learn in the Treatise Zevachim 90a, in the chapter commencing כל התדיר .

וכפר עליה, for during all the days that she had been excreting blood her thoughts had been preoccupied with the phenomenon of semen, etc, and she had therefore not been in a fit state of mind to enter the precincts of the Temple and offer sacred matters.

[The verse] placed it first. Meaning: For the purpose of reading the Torah that the one who reads in the Torah will read the word “burnt-offering” first, “but as to [the order of] offering...” [You might ask:] Why does Rashi not explain this above, where it is written: “She shall bring a lamb, in its first year, as a burnt-offering and a young pigeon or a turtledove as a sin-offering”? This is because above it is logical that it should place the burnt-offering first, since it is speaking about a rich person who brings a lamb as a burnt-offering, and a young pigeon or a turtledove as a sin-offering, and even for bringing the offerings the burnt-offering comes first, since a lamb is more important. Here, however, [it is speaking] of a poor person who brings two turtledoves or two young pigeons, which are both the same, so I might think that also for bringing the offering the burnt-offering comes first since it was placed first, etc. Therefore, Rashi explains: “The verse placed it first...”