Yaakov hears that Yosef is still alive and exclaims, "I will go and see him before I die!" (45:28). The next verse tells that indeed, Yaakov took his family and all his belongings and embarked on his trip. Instead of proceeding directly to Egypt, however, "he came to Be'er Sheva, where he offered sacrifices to the God of his father Yitzchak." Why did he stop in Be'er Sheva to bring sacrifices rather than traveling straight to Egypt?
One answer suggested by many commentators arises from the prophecy Yaakov receives while in Be'er Sheva: "God called to Yisrael in a vision by night… And he said, I am God… Fear not going down to Egypt… " (46:2-3). Apparently, Yaakov stopped over in Be'er Sheva because he was afraid to go to Egypt. Why? A wide variety of possibilities appear in the commentaries; the Abarbanel himself suggests six reasons why Yaakov may have feared. The Ramban suggests that Yaakov knew that his descent to Egypt marked the beginning of the exile, and he needed divine encouragement that his offspring will survive the grueling conditions of bondage. In a slightly different vein, the Midrash Hagadol and Rabbenu Yosef Bekhor Shor explain that Yaakov sought to receive God's permission before leaving Eretz Yisrael. After all, back in Parashat Toledot, God forbade his father Yitzchak from leaving Canaan to escape famine (26:2-3).
An entirely different approach is taken by the Netziv, in his "He'amek Davar." According to the Netziv, Yaakov had no intention of moving to Egypt at this point in time. He planned to go and see Yosef "before I die," at some point before his death, though not now. Instead, his renewed vitalization - "the spirit of their father Yaakov was revived" (45:27) - prompted his proactive response to the grave famine from which his family suffered. Rather than purchasing grain from Egypt, he decided instead to move to Be'er Sheva, just as his father had done when famine struck. There Yitzchak had enjoyed agricultural success and economic prosperity despite the harsh conditions (26:12). Yaakov followed this example and relocated in Be'er Sheva. He first offers sacrifices to "the God of his father, Yitzchak" to pray for the same success his father had enjoyed. Only when God appeared to him and urged him to continue onward to Egypt did Yaakov take his family to see Yosef.
Truth be told, this approach of the Netziv appears to be the simple meaning of a Midrash with which we are very familiar. We recite in the Haggadah that Yaakov and his family went to Egypt "annus, al pi ha-dibbur" - against their will, by divine decree. On the surface, it seems that Yaakov settled in Egypt only to obey God's command; otherwise, he would have stayed in Canaan.
Other commentators, who adopt the more conventional reading that Yaakov willingly moved to Egypt, presumably understood this Midrash differently. God orchestrated events in such a way that Yaakov and his family were practically grabbed from Canaan - by force of circumstance - and forcibly transferred to Egypt. Though they were not directly commanded to leave Canaan, the sequence of events that unfolded practically forced them into relocating in Egypt, such that God's decree of exile could be fulfilled.