Into the tent of Sarah his mother -
He brought her into the tent and she became exactly like his mother Sarah — as if it say, "And behold, she was Sarah, his mother!"
For while Sarah was living, there was a candle burning in the tent from one Sabbath eve to the next, there was always a blessing in the dough, and a cloud [of protection] was always hanging over the tent. But since her death all these had stopped. However, when Rebecca came, they reappeared” (Genesis Rabbah 60:16).
After his mother - It is natural that while a man’s mother is living, he is wrapped up in her, but when she dies he finds comfort in his wife (Pirkei DeRabbi Eliezer 32).