When Yaakov returned to Eretz Yisroel he "encamped" ("vayichan") on the outskirts of the city Shechem (Breishis 33:18). The rabbis of the Talmud (Shabbos 33a) understand the possuk to imply that in addition he improved and "beautified" the city, either by instituting a coin system, or a public bath house, or a shopping mall. The medrash understands yet an additional level of interpretation on the phrase "vayivhan", that Yaakov established his techum for Shabbos purposes[1]. The halacha declares that at the start of Shabbos each Jewish person has to determine where "his home" is, and has a very limited area around "his home" where he may roam about. Yaakov established his "home" and determined where his limited area of walking would be.
The Torah (Breishis 23:4) quotes Avraham Avinu as telling the bnei Chet (who lived in Kiryat Arba) that he was both a stranger and a regular citizen dwelling among them. These two terms are mutually exclusive! If one is a regular citizen, he is not at all a guest or a stranger - so how did Avraham describe himself as being simultaneously a stranger and a citizen? The answer obviously is that all religious Jews relate to the outside world about them in a dual fashion[2]. In many areas we work along with everyone else as full partners. We all use the world together and have a reciprocal obligation towards each other to make it more livable and more comfortable. When we were born we entered into a world full of beautiful trees, a world with hospitals, medications, etc. Therefore we all have an obligation to provide for such conveniences and institutions for the next generation[3]. All of mankind is considered one big partnership in a certain sense, just as people living in the same community are considered as belonging to a partnership, and are therefore obligated to contribute towards that partnership - in order to further develop it - in accordance with the wishes of the majority of the partners[4].
Yaakov Avinu, like his grandfather Avraham, felt obligated to establish shopping malls etc. to improve everyone's quality of living. Yes, we are all obligated to participate in all civic, scientific, and political enterprises which will enrich the lives of the entire community.
But at the same time the religious Jew has his own unique outlook on life and style of living. The tradition of the Talmud was, based on the possuk in Eicha (2:9), that although there is much chochma (knowledge and wisdom) to be gained from the secular world, but "Torah" (teaching a way of life and an outlook on the world) can not be picked up from the other disciplines. These can only be acquired through the revealed truths of the Torah.
Avraham Avinu says that although he is on the one hand a full-fledged citizen, at the same time he feels he is a stranger amongst his non -Jewish neighbors, and not only does he lead his life differently from them, even after death he may not bury his spouse Sara in the regular cemetery. Even in death, the Jew stands alone. And similarly Yaakov, despite the fact that he's so involved in improving the entire society, nonetheless he feels it necessary to chart out his techum, indicating that he can not "go out of his box" to mingle freely with all of his neighbors. He is absolutely unique and alone. The Torah mentions the fact that the Jewish people always stands alone (see Bamidbar 23:9), and this is linked (Devarim 33:28) to the "standing alone" of Yaakov Avinu.
Immediately after the mention of the fact that Yaakov wanted his family to stand alone, the Torah relates what tragedy followed (perek 34) when Dina decided to disobey her father's instructions and "hang out" with the local girls her age.
The Torah commanded us[5] ("u'shmartem es mishmarti" - Vayikra 18:30) to introduce safeguards to the mitzvos. Not only are we Biblically forbidden to carry in a reshush harabbim, we must also abstain from carrying in a karmelis, lest we forget and carry in a reshus harabim. Not only are we Biblically prohibited to eat meat cooked with milk, we should also avoid eating chicken with cheese, lest this will lead to eating real basar bechalav. Rabbi Moshe Chaim Luzzatto wrote in his classic work Mesilas Yesharim that the Torah's command to "erect a fence" ("asu s'yag laTorah" - Avos 1:1) about the mitzvos, to protect us from even coming close to sin, is not addressed only to the rabbis. Each individual must introduce personal "harchakos" (safeguards) depending on his or her particular situation.
The Torah relates (Breishis 35:2-4) that Yaakov disposed of all the avoda zarah (idols) in his possession which his children had taken from Shechem. The commentaries point out that avoda zarah ought to really be burnt. Why didn't Yaakov destroy them? The suggestion is offered (see Sforono) that the people of Shechem had already been "mevatel" these avoda zarahs, so strictly speaking, they had already lost their status of avoda zarah. Yaakov's disposing of them was a chumra that he thought appropriate in his circumstance.
A man like Yaakov who is very involved in the outside world, establishing shopping malls, etc., has to accept upon himself additional chumras and harchakos to prevent himself from being swallowed up by the secular society around him. One who sits in the beis hamedrash all day long, or who lives in Bnei Brak or Meah Shearim doesn't really need all such extra chumras or harchakos; he's no where near the secular world.
The same word ("vayichan") which indicates how Yaakov acted in accordance with the concept of "toshav" (a regular citizen of the world), also has the additional connotation of drawing the lines for isolation through techumin. We all have an obligation to strike a proper and reasonable balance between our status as ger and toshav; and the more one functions as a toshav, the more that individual must personally emphasize that he is at the same time really a "ger".