On the verse of Megilas Esther (4:16)
אשר לא כדת וכאשר אבדתי אבדתי
the Talmud (Meg 15a) says that Esther said, she was going to "violate the Law, because now she was going to intentionally" having an adulterine relation, and [then(?)] "she could not return to her husband"
שלא כדת היה שבכל יום ויום עד עכשיו באונס ועכשיו ברצון כאשר אבדתי מבית אבא אובד ממך
Why this was considered ברצון , she did not go to Achashveirosh in intent of having a relation, she just invited him to a meal?
If it was an issur, so why she did it? And Mordechai even asked her to do so.
So, was there an "heter"? Which? Giluy arayos is יהרג ואל יעבור isn't it? We sometimes hear the notion of להציל כלל ישראל ; is there a difference between a lonely יהרג ואל יעבור and a global one?
And if there was an heter, combined with לא תעמוד על דם רעך , it probably became an obligation; so, why was Esther prohibited to Mordechai? She had no choice and should be considered oness! She even should not be considered מעלה באישה , because her husband also agreed to do so? See also Kesuvos 19a,
השתא אילו אתו לקמן לאימלוכי אמרינן להו זילו חתמו ולא תתקטלון והשתא דחתמו אמרינן להו אמאי חתמיתו
Some thoughts from the discussions below:
On 1: Can we link this with פסיק רישיה ? (So why she was still permitted after saving Achashverosh from Bigtan&Teresh?...)
On 2: Was this kind of aveira lishma, as Talmud (Nazir 23a) says about Yael?