Yevamot, Chapter Ten, Mishnah Two
This mishnah continues to discuss the situation of a woman who was told that her husband was dead and she remarried, and then her husband returned.
1) If she married with the authorization of the court, she must leave, but is exempt from bringing a sacrifice.
a) If she married without the authorization of the court, she must leave and is liable to bring a sacrifice.
b) The authority of the court is thus more greater in that it exempts her from the sacrifice.
2) If the court ruled that she may be married and she went and disgraced herself, she must bring a sacrifice, because the court permitted her only to marry.
Section one: If she asked the court before she remarried, and they allowed her to remarry, she must leave her second husband, should her first husband return (she cannot return to her first husband either, as we saw in mishnah one). However, she is not liable to bring a sacrifice (sin offering) since she acted with the courts permission. It is as if the court takes upon itself the responsibility for her accidentally having sinned.
However, if she acted on her own without permission, she must bring a sin offering. The reason that she is able to bring a sin offering to atone for her sin is that her sin was unintentional; she didnt know her husband was alive when she married someone else. Had she sinned intentionally, an offering would not have been effective.
Section two: If the court ruled that she could remarry and she disgraced herself by marrying someone forbidden to her, for instance if she was a widow and she married the high priest, or if she was a divorcee and she remarried a priest, etc., she is liable to bring a sacrifice. When the court allowed her to remarry, the intention was a permitted marriage. By marrying someone not permitted to her, she is actually marrying on her own accord, and is therefore liable to bring a sacrifice as an unintentional sinner. Note that the sacrifice is for the adultery and not the forbidden marriage. Most forbidden marriages are not atoned for by sacrifices.