What does the Pasuk mean when it writes that there was "Tzayid b'Fiv"? In whose mouth?
Rashi #1, Targum Onkelos and Rashbam: There was venison in Yitzchak's mouth - meaning that Esav would constantly supply his father with venison.
Ramban #1: What the Pasuk means is that Yitzchak loved Esav because the venison which he loved, and was all that he ate, was brought to him by Esav.
Ramban #2: Because Esav constantly fed his father, his father called him 'Tzayid," after his deeds. 3
Malbim: Esav would tell him about his mighty hunting acts. 4
Gur Aryeh: How is this inferred from the Pasuk? According to its simple sense (that Yitzchak would eat of the animals that Esav trapped); the verse should have said 'l'Fiv' - into Yitzchak's mouth.
Oznayim la'Torah: Rashi's two explanations are really one and the same, since, it was because Esav provided him venison in his old age, that he became blind (both literally - refer to 27:1:1:7 - and figuratively) and failed to see through Esav's falsehoods.
Like David ha'Melech wrote about himself (in Tehillim 109:4) "va'Ani Sefilah" (for he constantly prayed).
Why would this cause Yitzchak to love him? Perhaps he thought that he must be very worthy for HaSh-m to grant him such abilities. (PF)
Our Sages teach us that Esav excelled at honoring his father; and we find similar deeds of other Gentiles as well (e.g. Dama ben Nesinah - Kidushin 31a). How did this come about?
Maharal #1 (Chidushei Agados Vol. 2, p.137, to Kidushin 31a): In Halachah, honor to one's teacher takes presence over honoring one's father, for one's father brought him only to this world, etc. Gentiles will more readily honor their parents, for this world is their environment - and for Esav in particular.
Maharal #2 (ibid. p. 138): Honoring parents is dictated by both logic and justice. They do not have traits that would allow them to concede on that which justice requires.
Maharal #3 (ibid.): One's parents created one's Guf; and HaSh-m provides the Neshamah. Their main focus is the Guf, whereas ours is the Neshamah.
Maharal #4 (ibid.): A son is obligated to his father by Midas ha'Din, and Gentiles associate with this trait.
Does the verse mean that Yitzchak did not love Yaakov?
Seforno: Not at all! It is just that, despite Esav's evil, he loved him too - knowing full well that he was not as righteous as Yaakov. 1
Ha'amek Davar: Also Yitzchak understood that Avraham's seed will be called through Yaakov. He loved Esav for serving him like a slave, and he benefited from this. Yaakov sat in the tent, and did not serve him much.
Gur Aryeh: Refer to 27:21:151.1:2.
Why did Rivkah love Yaakov and not Esav?
Seforno: Because she saw through Esav and was not taken in by his flattery. 1
Rashbam: Because she acknowledged Yaakov's Temimus, and following what HaSh-m told her that "The older one would serve the younger one." 2
Ohr ha'Chayim #1: Esav tricked only Yitzchak, for he feared his curse and hoped to get his Berachah.
Ohr ha'Chayim #2: According to Targum Onkelos, that Yitzchak loved Esav because he used to feed him venison. This was not so important to Rivkah, for Yitzchak was obligated to feed her like she was used to. Besu'el was very important in Aram, so she was used to eating well.
Malbim: She heard that the older will serve the younger, and recognized better the youths' natures.
The Oznayim la'Torah attributes this to the fact that she had seen it all in her brother Lavan - whom Esav resembled (refer to 25:20:2:2) - as opposed to Yitzchak, who never saw such behavior in his parents' house.
The Rashbam adds that this Pasuk is an introduction to the following Parshah, where Yitzchak attempts to bless Esav, and Rivkah tricks him into blessing Yaakov.
Since Rivkah knew about Yaakov's Tzidkus and Esav's evil; why did she not enlighten Yitzchak with the true facts?
Ramban 1 : It was part of HaSh-m's plan that Esav should hate Yaakov to serve as his rod to punish Yisrael throughout history. For this to happen, HaSh-m made sure (a) that Yitzchak remained unaware of Esav's evil until after he had blessed Yaakov, and (b) that it should not occur to Rivkah to divulge the truth to her husband.
Ohr ha'Chayim: Esav tricked only Yitzchak, for he feared his curse and hoped to get his Berachah. Perhaps he tricked him not in front of Rivkah, and she did not know why Yitzchak loved him.
Ha'amek Davar: Refer to 24:62:1:7*.
Why does it say that Yitzchak loved "Es Esav" (with the definite article)? The Torah commands to love "l'Re'acha Kamocha" (lit. to your fellow - Vayikra 19:18).
Ha'amek Davar: "Es" refers to loving in the heart. The prefix Lamed refers to fulfilling the person's desire.
Why does it say that "Yitzchak loved Esav" in the past tense; and "Rivkah loves Yaakov" in the present?
Ha'amek Davar: Rivkah loved Yaakov for his attributes. Also, it increased every day; one who learns Torah at night, Chesed is stretched over him during the day (Avodah Zarah 3b). Yitzchak's love for Esav was happenstance, at the time. Indeed, at the end it departed (refer to 28:8:1:4*)!