After Yaakov received the delightfully shocking news that his son Yosef was alive and well in Egypt (and gainfully employed!), the Torah records his gut reaction. 'And Yisrael said: How incomprehensible it is that Yosef is still alive. I will go down [to Egypt] and see him before I pass away." Sometime thereafter, the patriarch took a more thoughtful approach to his predicament, and a monstrous predicament it was.
Could Yaakov take leave of the Holy Land so easily? Indeed, Canaan was his permanent home. Even generously granting a liberal dispensation to be reunited with his long lost son - Egypt's viceroy - was the matter a trifling one? Hadn't Hashem come to him in a ladder vision years earlier promising him exclusive title to the land? Could/should he walk away from it now - even for all of the natural and good reasons like setting his pining eyes on his beloved Yosef?
Straining, Yaakov fretted and deliberated, mulling and dissecting the issues from each and every conceivable angle. He looked to his ancestors Avraham and Yitzhak for precedent. Clarity, in the form of divine communication, descended upon the distraught patriarch. As with the ladder prophecy so too this one soothed an aching soul. It came to provide him existential relief but not before he had packed up his family and belongings in Chevron and began journeying towards Egypt.
When the forefather and his family arrived in Beer Sheva 'he sacrificed sacrifices to the Almighty of his father Yitzhak.'
Students are correct to ask: Why did Yaakov solely sacrifice to the God of his father, and glaringly did not also invoke his grandfather Avraham's merit when addressing God?
Let us respond. Yaakov had a deep-seated fear of leaving the Holy Land - even for a brief spell. Egypt's libertine lifestyle and degenerate value system presented obvious impediments on a man of faith. True, Avraham sojourned to there in times of drought but those circumstances were different (the first patriarch had not yet entered into the circumcision covenant and also had not triumphed over the Akedah test). Thus, Avraham's example could not necessarily be applicable. Yitzhak had also faced a famine but had been prohibited by Hashem to leave Israel. By invoking Yitzhak's name here, Yaakov hoped and prayed to Hashem that He would not scuttle his plans to visit his son before dying. In effect, he petitioned for a hardship waiver.
Divine dispensation was granted. 'I am your father's Almighty.' That is, despite Hashem's strict, former warning to Yitzhak not to leave Israel, permission was presently granted to Yaakov. 'Do not fear traveling to Egypt.' Hashem promised protection for Yaakov and his descendants.