What does the Pasuk mean when it writes that "Yitzchak brought Rivkah to the tent of Sarah his mother"?
Rashi: It means that Rivkah was the exact replica of his mother Sarah, inasmuch as the three constant miracles that occurred in the tent when his mother was alive and which ceased when she died, returned when Rivkah arrived 1 - the Shabbos lamp burned the entire week, there was Berachah in the dough and a cloud of protection hovered over the tent. 2
Ramban: When Sarah died, [Avraham and Yitzchak], out of the high esteem in which they held her, declined to pitch her tent, so that no other woman should enter her tent. However, when Rivkah arrived, Yitzchak was comforted after his mother, and he allowed her to replace her. 3
Ramban (citing Targum Onkelos): He brought Rivkah to his tent and she was Sarah his mother - to teach us that he loved her due to her righteousness and good deeds, via which he was comforted after his mother. 4
Malbim: He did not marry her until he took her into Sarah's tent to see how she would act there, and saw that she was righteous like her.
Why does the Torah find it necessary to tell us that Yitzchak loved his wife?
Rashi: This teaches us that, as long as a man's mother is alive, he is bound to her, and that when she dies, he is comforted by his wife.
Ramban: The Torah informs us that he loved his wife and was comforted after his mother, to convey the deep pain he felt at the death of his mother, 1 a pain that left him only after he married Rivkah.
Oznayim la'Torah: To teach us that love comes after marriage, and not the other way around. 4
Why does it say that he took her?
Refer to 24:67:1:4.
Ha'Emek Davar: He was Mekadesh her again, for mid'Oraisa, Eliezer's Kidushin was invalid. A slave cannot be a Shali'ach for Kidushin. It helped only to designate her for Yitzchak. This suffices to obligate Bnei Noach Misah for her.