Genesis 12:10-13 reads:
There was a famine in the land, and Abram went down to Egypt to sojourn there, for the famine was severe in the land. As he was about to enter Egypt, he said to his wife Sarai, "I am well aware that you are a beautiful woman. When the Egyptians see you they will say, 'She is his wife,' and they will kill me, but let you live. Say then that you are my sister, that it may go well with me because of you, and that I may remain alive thanks to you."

Medieval Jewish commentators debated whether Abram did the right thing by leaving the land that God had promised to him. Ramban, for example, wrote:
Know that Abraham our father unintentionally committed a great sin by bringing his righteous wife to a stumbling block of sin on account of his fear for his life. He should have trusted that God would save him and his wife and all his belongings, for God surely has the power to help and to save. His leaving the Land, concerning which he had been commanded from the beginning, on account of the famine, was also a sin he committed, for in famine God would redeem him from death. It was because of this deed that the exile in the land of Egypt at the hand of Pharaoh was decreed for his children.1

Rabbi Levi ben Gershom (1288-1344), known in Western literature as Gersonides and in traditional Jewish by his acronym Ralbag, saw the matter differently. In fact, not only is Ralbag's view of Abram's actions diametrically opposed to that of Ramban, it is also conceptually distinct from that of precursors such as Radaq who maintained a positive opinion of Abraham's descent into Egypt.2 In his commentary to Tanach, Ralbag composed as series of "useful lessons" (to'alot) to each section that he commented on. In his commentary to the Torah, he divided his lessons into those that pertain to commandments (mitzvoth), doctrinal opinions (de'ot) and ethics (middot). Ralbag devoted several ethical lessons to the benefits one receives from studying the particular parashah of Abraham's descent into Egypt and its aftermath. His first useful ethical lesson on this matter reads as follows:
A man should obtain food and similar necessities needed for bodily preservation with haritzut. God had already promised Abram success with respect to the acquisition of possessions. Nonetheless, Abram aroused himself because of the famine that existed in the land of Canaan to go to the land of Egypt, and did not desist from going there because God, may He be exalted, had (previously) commanded him to dwell in the land of Canaan.

For the commandments of God, may He be exalted, are to bestow good upon man, not that he would die because of them. And because of this Abram knew the will of God, may He be exalted, was that he should turn away from there (Canaan) for the pursuit of food.

Moreover, the intention of Abram's journey to the land of Canaan was in order that he should be more prepared to receive the Divine overflow that would cling to him, and this would not be conceivable in a state of famine and lack of food. And for this reason it was the greater good that he (Abram) should leave that place (Canaan) to the place where food would be found-until the famine should cease.3

Ralbag's next useful ethical lesson deals with the fact that Abram placed his wife in danger of violation by Pharaoh. Abram, in order to save his life, did not mention that Sarah was his wife but presented her as his sister. Ralbag writes:
A man must plan ahead4 with haritzut regarding future matters. If one first discerns what (future unfortunate event) might happen and then settles upon a plan (to avoid it), as a result he will escape potential misfortune. But if one does not first look ahead, the haste5 that will characterize his plans will make it impossible for him to obtain good results. Plans will not be successful if one does not patiently look ahead (at what might happen). Abram the perfect (shalem), before he entered Egypt, endeavored to plan ahead because of the possibility that he might suffer misfortune due to his wife's beauty.6

Ralbag gave the rabbinic dictum that one may tell a lie in order to preserve peace his own twist. This ethical lesson fortifies Ralbag's understanding of the lesson that is learnt from the narrative of Joseph's brothers. They told an untruth to their brother concerning their deceased father Jacob, in order to preserve family peace.
It is appropriate for a man to endeavor to achieve peace as far as possible. Its benefits are wonderful for both family and society. Hence, it is inappropriate for a man to care if peace is achieved by a somewhat repugnant action such as lying. It is inappropriate that the desire to stay far away from lies be able to thwart the noble goal of peace. Joseph's brothers told an untrue story concerning their father's wishes in order to achieve peace between Joseph and themselves. For this reason our Rabbis, of blessed memory, stated that it is permitted to tell an untruth for the purpose of peace (Yebamot 65b). In another place they stated that it is a meritorious act (mitzvah) to tell an untruth for the purpose of peace (ibid.).7

Moreover, according to Ralbag, peace is a wonderful virtue because it allows men to develop and actualize their intellects. Joseph's brothers were acting as prudently as their great-grandfather Abraham did.
The various passages concerning Abraham and Joseph that we have just cited underscore the theme that one must act with haritzut to obtain the proper conditions necessary for the possibility of personal intellectual attainments. In these passages, Ralbag does not mention the tension that can arise between social/political benefits and individual benefits that flow from the exercise of haritzut. What happens in a scenario where one's personals goals conflict with those of society as a whole, or of other specific individuals? Are virtuous biblical figures cast in the mold of men whose actions are exclusively motivated by the desire to preserve the self and philosophize? How does the Gersonidean view of societal ethics reflect itself in his biblical commentaries? These issues lie beyond the scope of the discussion here. What can be asserted, however, is that Ralbag sees assertive human efforts in a positive vein. Reversing a popular medieval epigram that asserted the futility of human efforts, one can say that according to Ralbag, ha-haritzur emet. In other words, diligence, human effort, zeal is indeed true, that is, worthwhile and praiseworthy in the eyes of God.

[1] Ramban (Nachmanides): Commentary on the Torah: Genesis, ed. Charles Chavel (New York, 1971), pp. 173-74.
[2] See our section, "Miracles versus Haritzut" below.
[3] Commentary on the Torah, Genesis, useful lesson #1 following Gen. 13:18 (a comment regarding Gen. 12:10), Braner ed., p. 202.
[4] Hebrew, laqahat 'etzah (literally, to take advice). Ralbag does not imply here that Abram consulted any other person, even Sarai, before deciding what to do. He simply told Sarai of his plan.
[5] See our section, "Impetuousness as a Threat to Self-Interest: the Case of Reuben," below.
[6] Commentary on the Torah, Genesis, useful lesson #2 following Gen. 13:18 (corresponding to Genesis 12:10-13), Braner ed., pp. 202-03.
[7] Commentary on the Torah, Genesis, useful lesson #13 following Gen. 50:26, Braner ed., p. 564.