When he prepares to go down to Mitzrayim, Yaakov is told by Hashem that יוסף ישית ידו על עיניך, meaning that he should not worry about being affected in the moral abyss of Galus because Yosef will cover his eyes, and protect him (בראשית מ"ו:ד'). Why, however, is it necessary for Yaakov to require any protection? After all, Yaakov survived spiritually on his own in the house of the ultimate trickster - Lavan the Arami! What necessitated this special protection to be provided by Yosef against the ills of Egyptian society?
One of the main evil characteristics of the Egyptians, according to the Midrash, was that they did not recognise the hand of Hashem. Because of the natural overflowing of the Nile River, they did not have to work hard in order to provide for their needs. The existence which they led may be compared to that of Adam and Chava in Gan Eden, who benefitted from fruits which grew and reproduced on their own. But once they ate from the Eitz HaDa'as, they had to leave the Gan and this carefree lifestye behind forever. Those who lived in Mitzrayim, however, tried to recreate this state. This led them to fall to spiritual depths because they took everything for granted. Yaakov feared being influenced in this way.
Avraham was a scientist. He discovered G-d through looking at the stars. **** is a new ***** - development from *****. He discovered G-d by being a ****** **** - by learning Torah. **** is a new ***** from ***** and ****. He believed in both the steady learning of Torah and research of the outside world. Essentially, Yaakov felt that he should learn Torah all day. We may presume that he wanted to be in a Gan Eden-like state, but this could only be accomplished in Eretz Yisrael. Once Yaakov was in Lavan's house, he felt that he had to strengthen his commitment to Hashem by educating himself about the beauty of Hashem's world. Therefore, Yaakov became a רועה צאן, a shepherd; he studied the outside world, representing the glory of Hashem, just as his grandfather Avraham did, in order to keep true to the path of Hashem in the outside world. But as soon as Ya'akov came back to Eretz Yisrael, he reverted back to being a יושב אהלים. This may be inferred from the fact that while his sons were working with the sheep in Shechem, Yaakov was not with them and had to send Yosef to them. Possibly, not only was he not working with them, but he in fact had distanced himself from them.
Many years later, when Yaakov heard that Yosef was alive, he was overjoyed and naturally wanted to see him. But that was before he reached Be'er Sheva. Be'er Sheva was the place where Yitzchak had redug the wells of Avraham, which symbolized his desire to keep the ideas of Avraham alive. He did this by learning Torah in order to master his father's teachings. But the Sforno notes that Yitzchak was not permitted to leave Eretz Yisrael, presumably because he would not have been able to survive Jewishly in the face of outside influences. Yaakov suddenly became nervous. Should he continue on to Mitzrayim? Hashem reassured him that he could go, and would be able to continue the traditions of his father. To shield him from the Egyptian society, Yosef would "cover the eyes" of Yaakov. He would make sure that Yaakov would not return to a Gan Eden -like state. Yosef, the one who remained committed to Hashem even in Mitzrayim, the one who conquered the servant world by becoming the viceroy of Egypt, would protect Yaakov.
From this, we may learn a very important lesson based on the principle of מעשה אבות סימן לבנים, that the actions of our ancestors contain a message for their descendants. In order to maintain our commitment to Hashem in Galus, exile from Eretz Yisrael, we must comprehend and educate ourselves regarding the beauty of Hashem's world, whether through the sciences, history, philosophy, or other fields. If we use these disciplines in order to increase our dedication to Torah, then we should survive the Galus spiritually, just as Yaakov did in the house of Lavan, and Yosef did in Mitzrayim. We do not have a Yosef to advise us, as Yaakov did in Mitzrayim. We therefore must shield ourselves with Torah, proper study of Hashem's world, and rely on the support of Hashem.