John Calvin Commentary Leviticus 12:4

"And she shall continue in the blood of [her] purifying three and thirty days; she shall touch no hallowed thing, nor come into the sanctuary, until the days of her purifying be fulfilled." — Leviticus 12:4 (ASV)

And she shall then continue. The uncleanness of seven days for a male, and fourteen days for a female, refers to the hemorrhage, as we will also see elsewhere regarding the menstrual discharge. For the rest of the time, she is forbidden to participate in religious services and to approach the sanctuary (by which word the court is meant here), and so is considered unholy. This was not only so that she herself would lament her condition, but also that her husband, warned by the sight, would learn to abhor and detest original sin.

For this was a serious exhortation to repentance, when they acknowledged that they were contaminated in their offspring, in whom God’s blessing otherwise manifests itself.

The question now arises: why is the time of purification double for a female child? Some attribute this to a natural cause, namely, because the hemorrhage then lasts longer; and indeed, it was a part of chastity and continence that husbands should not then approach their wives. But since the purpose of this ceremony was different—namely, as an indication of the curse on the whole human race—we must look more carefully in this direction.

I do not know if the view some take is sound: that the mother is more defiled by female offspring because there is a greater disposition to vice in this sex. Perhaps it is more probable, as some think, that it was because the woman was the source of the rebellion when, being deceived by the serpent, she destroyed her husband with herself and drew her descendants into the same ruin.

But it seems more correct to me that the punishment regarding males was lightened and diminished by circumcision. For although in that symbol God consecrated both sexes, He nevertheless honored males with special favor by engraving His covenant on their flesh. Therefore, He also expressly mentions their circumcision, by which a dignity was imparted to them, which made them superior to females.

At the end of the chapter, consideration is given to the poor, lest, burdened by too great an expense, they might be made less ready to obey the Law. From this we gather that God does not care for outward pomp and wealth, since the humble sacrifice of the poor, according to their means, is no less pleasing to Him than the more valuable one of the rich.