We find in Tanach a reference to the “Sefer HaYashar - Book of the Straightforward”:
וידם השמש וירח עמד עד יקם גוי איביו הלא היא כתובה על ספר הישר.
The sun was silent and the moon stood still, until the nation was avenged of its enemies, as is written in the Book of the Straightforward.
The Gemara presents a debate over which volume of the Torah is called “the Book of the Straightforward.” According to R’ Yochanan, this refers to Sefer Bereishis, which chronicles the lives of our straightforward forefathers: Avraham, Yitzchak and Yaakov. According to R’ Elazar, this refers to Sefer Devarim, in which it is written, “And you shall do that which is straightforward and good in the eyes of Hashem.”
This debate portrays the essential difference between he who is straightforward at heart, and he who is straightforward in practice. A person may have the character trait of honesty, either having been born with a naturally truthful disposition, or having developed this trait by working on his middos over the years. However, it is not enough to have an honest character, unless one’s actions reflect his honest heart.
The same may be said of all good middos. A person must strive to be both good at heart and good in deed. For example, in one place, our Sages tell us that we must emulate Hashem. Just as He is gracious and merciful, so too must we strive to develop the traits of graciousness and mercy. Elsewhere, the Gemara states that just as Hashem clothes the naked, so too must we provide clothes for the poor. Just as Hashem visits the sick, so too must we. The first Gemara enjoins us to develop the traits of graciousness and mercy on a theoretical, emotional level, while the second Gemara enjoins us to put those traits into practice.
Some people are good at heart. They share the pain of the unfortunate, and are deeply moved by sympathy for the needs of those around them. However, being too lazy or busy with their own affairs, they never manage to put these sentiments into action, to help those in need. Other people do deeds of kindness, but only out of rote or social convention, since they have no real concern for those they help. Both kinds of people are lacking, since character perfection demands us to be good both in heart and in practice -emulating Hashem in all our ways.
In Sefer Bereishis, we learn about the Avos, our role models for honesty, integrity and all noble traits. However, it is insufficient for us to merely admire these traits, and theoretically espouse them. In Sefer Devarim we are commanded to “do that which is straightforward and good in the eyes of Hashem,” by emulating these traits in practice. Both are called Sefer HaYashar, since they portray equally important, complementary aspects of straightforwardness.
The Rambam writes as follows:
ולא שבט לוי בלבד אלא כל איש ואיש מכל באי העולם אשר נדבה רוחו אותו והבינו מדעו להבדל לעמוד לפני ה' לשרתו ולעובדו לדעה את ה' והלך ישר כמו שעשהו האלהים ופרק מעל צוארו עול החשבונות הרבים אשר בקשו בני האדם הרי זה נתקדש קדש קדשים ויהיה ה' חלקו ונחלתו לעולם ולעולמי עולמים ויזכה לו בעולם הזה דבר המספיק לו כמו שזכה לכהנים ללוים. הרי דוד ,עליו השלום, אומר ה' מנת חלקי וכוסי אתה תומיך גורלי.
Not only the Tribe of Levi, but any person, from anywhere in the world, whose soul so inspires him, and his reason so directs him, to separate himself and stand before Hashem, to serve Him, to know Hashem, and to walk straightforwardly, as G‑d made him; casting off his shoulders the yoke of the many schemes of man; such a person is sanctified as the holiest of holies. Hashem will be his portion and his inheritance for all eternity, providing his needs in this world, as He provided for the Kohanim and Leviim. David, peace be to him, said, “Hashem, my portion and my cup, You support my fate.”
The Rambam notes three distinct traits that must be developed by anyone who wishes to devote his life to Hashem: to know Hashem – a reference to Torah study, since Hashem and His wisdom are One; to serve Him – a reference to the service of the Beis HaMikdash, or prayer, the service of the heart, which now takes its place; and to walk straightforwardly as G‑d made him – a reference to honesty and integrity in all one’s dealings. This is a basic human trait, which should be natural to us all, but has sadly been perverted by our selfish interests, as the possuk states, “G‑d made mankind straightforward, but they sought out their many schemes.”
Honesty is no mere social convention. It is an essential prerequisite for drawing close to Hashem. A person might make great progress in Torah study and prayer, yet it is absolutely impossible for him to draw close to Hashem unless he develops this third prerequisite of honesty and straightforwardness. In order for a person to be considered, “sanctified as the holy of holiest,” he must be honest in all his dealings.
The Rambam points to Yaakov Avinu as our role model for integrity in business:
כדרך שמוזהר בעל הבית שלא יגזול שכר עני ולא יעכבנו כך העני מוזהר שלא יגזול מלאכת בעל הבית ויבטל מעט בכאן ומעט בכאן ומוציא כל היום במרמה אלא חייב לדקדק על עצמו בזמן שהרי הקפידו על ברכה רביעית של ברכת המזון שלא יברך אותה, וכן חייב לעבוד בכל כחו שהרי יעקב הצדיק אמר כי בכל כחי עבדתי את אביכן, לפיכך נטל שכר זאת אף בעולם הזה שנאמר ויפרץ האיש מאד מאד.
Just as an employer is forbidden to rob the poor [employees] by withholding their wages, so too the poor [employees] are forbidden to rob their employer by shirking their duties, wasting a little time here, and a little time there, until finally the entire day is wasted in deceit. Rather, one must be punctual in his work time. For this reason, our Sages exempted laborers from reciting the fourth (Rabbinic) blessing of Birkas HaMazon.
A laborer must serve his employer with all his strength, just as Yaakov the Tzaddik said, “I served your father (Lavan) with all my strength.” For this, he was rewarded in this world as well (as the World to Come), as the possuk states, “And the man was very, very successful.”
Many other halachos are learned from the actions of our forefathers, but in this alone the Rambam chose to use the title “Tzaddik,” signifying that only by being honest in our business dealings, can we consider ourselves righteous servants of Hashem.
We pride ourselves on our accomplishments in Torah and mitzvos. We fancy that we are fit to bear the illustrious accolade of “Kingdom of Priests and Holy Nation,” that Hashem awarded us on Har Sinai. Perhaps we have indeed made great progress in the first two prerequisites of Torah and Avodah – yet, sad to say, it seems that we have much to improve in the third prerequisite, of yashrus – straightforwardness and integrity, without which we can hardly consider ourselves to be Tzaddikim – as the Rambam writes.
Have we “cast off our shoulders the yoke of man’s many schemes”? Or perhaps we are so immersed in our own selfish interests, that we hardly give a second thought to what is right and what is wrong, what is honest and what is deceitful. Our Torah is a Book of Straightforwardness, and Hashem created us to be equally straightforward. In this week’s parshah, we are presented with the Torah prohibition against being dishonest in business: וכי תמכרו ממכר לעמיתך או קנה מיד עמיתך אל תונו איש את אחיו – “’When selling something to your kinsman, or buying something from him, do not cheat your brother.” Only a person who excels in this crucial trait can hope to draw close to Hashem, as His portion and His inheritance for all eternity.
כי ישרים דרכי ה' וצדקים ילכו בם ופשעים יכשלו בם.
For the ways of Hashem are straightforward. The Tzaddikim walk in them, while the wicked stumble.
 Yehoshua 10:13
 Avodah Zarah 25a
 Devarim 6:18
 Shabbos 133b
 Sotah 14a
 Rambam, Hilchos Shemitta V’Yovalos, 13:13
 Taanis 2a
 Koheles 7
 Hilchos Sechirus 13:7
 Bereishis 31:6
 Bereishis 30:43
 Vayikra 25:14