My father, Rabbi Leon Eliezer Friedlander, Z”L, said the following concerning Rivka’s request to Yaakov that he dress up as Eisav, deceive his father, and receive the blessing. 

To paraphrase:

Why did Yaakov not tell his father Yitzchak that Eisav rejected the rights of the first born?  Yaakov could have been more direct with his father by telling him the truth?  Consider all of the trouble Yaakov Avinu underwent in avoiding Yitzchak Avinu finding out that Yaakov was not Eisav. Furthermore, Yaakov’s trials and tribulations from this matter continued to the point of having to flee his home from his brother’s wrath and live in exile for many years. Why?

My father answered that the reason Yaakov could not be straightforward with Yitzchak was all for the sake of avoiding the sin of loshon hora.  Since Yitzchak believed that Eisav was worthy of the blessings (Genesis 25:28), perhaps he would have rejected any charges leveled against Eisav and sadly might have viewed this statement as words of slander.

One could have asked my father, if Yaakov had to decide between his father’s honor and HaShem’s honor, HaShem must come first. (Yevamos 6a) Does not the Talmud tell us, better to be considered a fool one’s whole life than to be considered wicked in the eyes of Heaven even for a single moment? (Ediyos 5:6) Better to give ineffective protest than to walk on the path of deception, especially towards one’s own father?  And finally, a mitzvah that comes through a sin is not a mitzvah (Sukkah 30a)?

We could answer that if Yitzchak assumed that both Yaakov and Rivka were slandering a son worthy of a bracha, it would mean that Yitzchak would have been placed in a position of feeling forced to choose between one son and the other.

 
Rivka acted throughout for the sake of Bnai Yisrael, ensuring blessing and avoiding curses for Yaakov and his children.  Further, she wanted the truth to come out. Why should Yitzchak be mocked by Eisav’s trickery all of his life? Yitzchak deserved to know the truth, that Yaakov was the Tzadik of his children, not Eisav, as Rivka had always known (25:28)! 

Whereas Yaakov agreed with Rivka, his reasoning was that it was better that he (Yaakov) should live in exile for many years due to his evil brother’s anger, than to cause his hallowed father even one moment of emotional turmoil. 

It was only when Eisav exclaimed before Yitzchak regarding Yaakov’s rights to the first born status “he took away my birthright these two times!” (27:36) and thus incidentally and inadvertently revealing the truth, admitting Yaakov’s rights to the blessings. Only then did Rivka and Yaakov’s plan of minimizing troubles without succumbing to slander had come to full fruition and success. It was only then that Yitzchak’s blessing to Yaakov was permanently guaranteed.

Good Shabbos!