Rashi on TanakhLeviticus 12

When a woman conceives. R. Simlai said: Just as the creation of mankind [came only] after [that of] every animal, beast and bird in the Work of Creation, so too his teaching is explained [only] after the teaching [regarding] animals, beasts and birds.

When [she] conceives. [This comes] to include even [when the embryo] is born mushy — [that is, as though] it was crushed and became as semen — its mother [is ritually] unclean as if it were childbirth.

As the days of her menstrual flow shall she be unclean. According to the order of all impurity mentioned in regard to a menstruant woman, so is she made impure by the impurity of childbirth — even if the womb opens without [any visible] blood.

Flow, an expression of something which flows from her body. Another interpretation: An expression of illness and malady, for a woman does not see blood without becoming ill, and her head and limbs [feel] heavy.

She will remain. תֵּשֵׁב is nothing more than an expression of “remaining” as [for example] “You remained in Kadesh,” “He settled in the Plains of Mamrei.”

that the blood is ritually pure, [implying] that even if she sees [blood], she is [ritually] pure.

that the blood is ritually pure, without a מַפִּיק הֵא, and [so this word] is a noun, equivalent to טהַר .

The days of her purity. [The word טָהֳרָהּ has a] מַפִּיק הֵא, [meaning:] “the days of her purity.”

She shall not touch. A warning to one who eats, etc. as it was taught in [Maseches] Yevomos.

Anything holy. [The word “anything” comes] to include terumoh, for this one is [considered] as one who has immersed [in a מִקְוֶה, but whose purification is concluded only] after a long day. [That is,] she immersed at the end of seven [days], but her “sun” of purification does not set until sunset of the fortieth day; then she brings her purification atonement the next day.

He will bring it. This teaches you that [the omission of] only one of them prevents her from eating holy food, and what is that? That is the sin-offering, as it is said, “and the kohein will atone for her and she will be cleansed” — [the one] which comes to atone — [it is] on it that the purification depends.

And she will be cleansed. Therefore, [we learn] that until now she is considered unclean.

One as a burnt-offering and one as a sin-offering. The verse placed it first only for [the purpose of] reading [the Torah scroll], but as to [the order of] offering [the sacrifices], the sin-offering precedes the burnt-offering; so have we learned in [Maseches] Zevochim, in the chapter “Kol Hatodir.”