I am presently involved in the fascinating sugya of גדולה עבירה לשמה ממצוה שלא לשמה [Nazir 23]. Rashi explains that the Imahos did their mitzva שלא לשמה. What mitzva?
"שאמרו לבעליהן לבא אל שפחתן ולא לשם מצוה נתכונו אלא כדי שמתקנאות זו בזו, רחל באחותה ושרה ולאה באמהות".
How does Rashi know that the Imahos only told their husbands to be with their Shfachos out of קנאה? And what does Rashi mean when he says ושרה ולאה באמהות? Which Imahos?
See also the Kashya of the Be'er Sheva [Horiyos 10b] and his different conclusion.
Tosfos [Yevamos 103] says that the מצוה שלא לשמה of the Imahos was that they had הנאה from the מעשה ביאה with their husbands. Why is it automatically שלא לשמה if there is האנה? That is natural?! I understand that a תנאי for עבירה לשמה must be no הנאה [see Pachad Yitzchak Pesach 'מאמר נ] but if a mitzva is done with pure intentions and there is also accompanied הנאה what is the problem?? Why is that defined as שלא לשמה?
I am perplexed...
