What is the significance of the Berachah that Yitzchak gave Yaakov here?
Seforno: Yitzchak [initially] suspected that Yaakov was worthy of a curse, like Yaakov himself stated earlier, "v'Heveisi Alai Kelalah" (27:12). The Gemara says in Berachos (31b) that 'Someone who suspects his friend of something that he did not do must not only appease him, but bless him as well, like Eli blessed Chanah.' Ohr ha'Chayim - before feeling him, Yitzchak thought that Yaakov is Mesa'te'a (feigning to be Esav). Even a Chacham's resentment in his heart can bring a curse (Bava Metzia 84a). Yitzchak blessed him (when he concluded that it is Esav) to remove the effect of his prior resentment.
Malbim: Yitzchak's eating was the preparation for the Berachah. Just like offering a Korban puts Shechinah on the one who offered it, and through Kohanim eating, the owners get Kaparah, so Yitzchak's eating gave Divine power to Yaakov. Chazal said that the goats were a commemoration of Chagigah and Pesach.
Ha'amek Davar: He concluded that it is Esav; he changed his voice and mentioned HaSh-m's name to make it easier for Yitzchak to get Ru'ach ha'Kodesh - "b'Chol ha'Makom Asher Azkir Es Shemi..." (Shemos 20:21). He blessed him for this.