Commentary for Niddah 62:6

Why does the Torah say that a yoledet brings a korban? Although a zav also brings a korban because of the tumah emitted from his body, would that be true of a yoledet according to Rabbi Shimon (since he holds it's possible for the womb to open bloodlessly)? If so, what's the reason she brings a korban, and why is she less than someone who's tamei from a corpse or similar cases? And behold, also the leper and the nazir tamei bring a korban, even though the tumah isn't emitted from their bodies! In every case, they bring [a korban] on account of the sin; "due to seven things negaim come: and regarding the sin a soul has sinned, ..." see the first chapter of Tosefta Shevuot (quoted on Keritot 26a). Even though generally they don't bring a korban for these sins, in any case here they lead to tumah and so these [people] need a korban. This is not the case with a yoledet. For Rabbi Shimon this is a better question, and he teaches them that she too has sinned and it seems that this sin has caused the tumah, as I will explain if God wills it. For according to the Ra'avad, one who takes an oath not to eat matzah, if it is Pesach night this oath takes no effect even if it was a general vow, since at this moment it didn't take effect. And the poskim are divided about this. It seems to me that Rabbi Shimon, who does not include, everyone agrees that where one takes an oath on the night of Passover [to eat matzah] it does not take effect, even if [the oath was] regarding the entire year. This being so, we say that for this the yoledet was forbidden to her husband -- for it was revealed to the Blessed Name that she crouches [in birth] and takes an oath not to have sex with her husband more. For this reason, [the Torah] forbids her to him, and it turns out that her oath has no effect since it's in addition to an existing prohibition - and since it takes no effect now, it also does not take effect after some time has passed [i.e. even after she exits the status of yoledet and the Torah no longer forbids her to her husband, the oath remains null]. And it turns out that this is also settled for the leniencies[?] of Rabbi Yosef, that an oath requires a korban to be brought - this says that there's no "explicit" pronunciation, for behold the oath never took effect. So, only with the oath in vain is there a problem, for every oath which does not take effect is an oath in vain. And let it be that generally a korban is not brought for an oath in vain, but here, since it causes tumah for her to her husband, he also brings a korban as is written above in the name of the Tosfot regarding the leper and the nazir tamei. So for Rabbi Yosef there's a difficulty, why do we have an inclusive prohibition, and for him it's an explicit oath? But for us it's fine, we don't need any reason why it's needed to bring a korban since it's impossible to open the womb without blood, and that's tumah which is emitted from her body, and therefore she's like a zav who brings a korban, and this is easy to understand.