Why did Esav have to bring his father venison in order to receive the Berachos?
Seforno: Clearly, although Yitzchak did not see through Esav, he did not consider him automatically worthy 1 of the Berachos. 2 Consequently, he made him first work to bring him food, to fulfill the Mitzvah of Kibud Av, against which he would merit the Berachos. 3
Chizkuni, Moshav Zekenim, Sha'alos u'Teshuvos Maharam: So that Yitzchak should bless him with a full heart, because the Shechinah only rests on a Lev Shalem and where there is Simchah. 4
Oznayim la'Torah: Because it is essential for the Mevarech to see the person he is blessing, 5 and, due to his blindness, Yitzchak could not see Esav while blessing him, he made up for the deficiency by applying the other four senses; Taste - He ate from his venison; Hearing - he asked him "Mah Zeh Miharta Limtzo, Beni?," in order to hear his reply; Touch - he felt him to substantiate that his hands were hairy. Smell - he smelt the aroma of his clothes.
Malbim (to 27: 3,4): A Berachah requires (a) that the recipient prepare himself; (b) the giver rise and cling to the Source of Berachah; (c) connection between the giver and the recipient. Esav would prepare himself through Kibud Av, for which the Torah promises long life. To reach Devekus, Yitzchak would eat. This is like a bribe to the body to allow the Nefesh to leave (unlike its nature) and cling to spirituality. Making the food the way I like and giving to me is for the connection.
When he blessed Yaakov, on the other hand, he did not ask him for anything, because he knew that Yaakov was worthy of the Berachos anyway.
As the Gemara says in Shabbos 30b.
Oznayim la'Torah: Since sight is the most powerful of all the senses, it is therefore the one with which one connects the most with the person who is being blessed, thereby enabling the Berachah to take full effect. See Oznayim la'Torah, who elaborates on this point.
Which Berachos did Yitzchak plan to bestow upon Esav?
Ramban and Rashbam 1 : The Berachos of Avraham, to inherit Eretz Kena'an, and that he would be the one to enter into the covenant with HaSh-m - because, as far as Yitzchak was concerned, Esav was the Bechor.
Moshav Zekenim (to 27:3): From the Berachos that Yitzchak (knowingly) gave to Yaakov (to be a great nation, Birkos Avraham, and Eretz Kena'an - 28: 3,4), we infer that he knew Esav's nature. 2 (His first Berachos to Yaakov were what he planned to bless Esav - dew, fertile land, grain, wine, and to rule over his brothers.)
If so, why did he want to eat from his Shechitah, and bless him? He wanted to bless him due to appreciation for endangering himself in order to feed him. Lev Eliyahu (Bereishis, p. 107) - Yitzchak feared to bless Yaakov monetarily, lest he engage in matters of this world and wax rich, and his Shleimus will be blunted. Rather, he intended to make Yaakov and Esav like Yisachar and Zevulun.
Why did Rivkah not tell Yitzchak about the prophecy (that preceded the birth of the twins) "v'Rav Ya'avod Tza'ir" (25:23)?
Ramban #1: Initially, it was not correct for her to tell Yitzchak about it - particularly as she went to ask HaSh-m without his permission. Now she did not, because she realized that, due to his love for Esav, he would not bless Yaakov, rather, he would leave [the Berachos] in HaSh-m's hands. Rather, [she told Yaakov to pretend to be Esav,] so Yitzchak would bless Yaakov with a full heart.
Ramban #2: She thought that Yitzchak was a greater prophet than the one who informed her (Shem), in which case it was not necessary to inform him.
Ramban #3: It was min ha'Shamayim that she should not tell him, so that Yaakov should receive these Berachos; and Esav, those of "Al Charbecha Tichyeh" (27: 39-40).
Ha'amek Davar: Refer to 24:62:1:7*.
Malbim: She would have tried to convince him, but she knew that Esav went "l'Havi" (he will return promptly - refer to 27:5:2:1), so there was not time for this.
Perhaps she did tell him! The verse is ambiguous. It could mean that the younger will serve the older (see Ibn Ezra to Shemos 10:8, Radak to 25:23; refer to 25:23:3). Yitzchak understood so, due to "Ki Tzayid b'Fiv" (25:28). Rivkah grew up among Resha'im and recognized Esav's evil. She was sure that the older will serve the younger. (PF)
Yitzchak was a Navi, but she had to go to Shem to hear "v'Rav Ya'avod Tza'ir" (25:23). She reasoned, 'If HaSh-m does not want to reveal it to Yitzchak, how can I reveal it?!' 1 (PF)
Why did Yitzchak say "va'Aseh Li Mat'amim... v'Havi'ah Li"?
Ha'amek Davar: Make the food with intent for me, so you will have more merit. After preparing it in my house, bring it to my room.
What is "Tevarechecha Nafshi"?
Ha'amek Davar: It is my desire.