Shoftim, Devarim 18:13. Insider Trading and Showing Your Work. תמים תהיה עם ה' אלקיך

What does the Torah want when it warns us not to seek to know the future?
Rashi brings from the Sifri

 התהלך עמו בתמימות ותצפה לו ולא תחקור אחר העתידות, אלא כל מה שיבא עליך קבל בתמימות ואז תהיה עמו ולחלקו

 Conduct yourself with Him with simplicity and depend on Him, and do not inquire of the future; rather, accept whatever happens to you with [unquestioning] simplicity and then, you will be with Him and for His portion.

Rashi, by saying that any attempt to divine the future is not proper, is very different than the Ibn Ezra, who sees the warning as limited to seeking knowledge from kishuf and the like.  The ibn Ezra says

ההולכים אל בית הקברות ולוקחים עצם אדם מת ובעבור מחשבתו ושגיונו תראה לו דמות צורות בחלום גם בהקיץ וכל אלה תועבות השם כי האמת להיות לב האדם תמיד תמים עם בוראו וכאשר ישען על חכמתו לבקש האמת ומה שיהיה חוץ מהשם הנה לבו חסר כי הוא משובש והרוצה לדרוש ידרוש מהשם על פי הנביא על כן כתוב אחריו נביא מקרבך

Rashi is also different than the Ramban here, who says that the problem is that you mustn't think that the stars foretell your fate- you must remember that ein mazal li'yisrael, and tefilla is all that matters.

שנייחד לבבנו אליו לבדו ונאמין שהוא לבדו עושה כל והוא היודע אמתת כל עתיד וממנו לבדו נדרוש העתידות מנביאיו או מאנשי חסידיו רצונו לומר אורים ותומים ולא נדרוש מהוברי שמים ולא מזולתם ולא נבטח שיבואו דבריהם על כל פנים אבל אם נשמע דבר מהם נאמר הכל בידי שמים כי הוא אלהי האלהים עליון על הכל היכול בכל משנה מערכות הכוכבים והמזלות כרצונו מפר אותות בדים וקוסמים יהולל ונאמין שכל הבאות תהיינה כפי התקרב האדם לעבודתו ולפיכך אחר אזהרת שאלת העתידות מקוסם ודורש בעד החיים אל המתים אמר שתהיה תמים עם השם בכל אלה ולא תירא ממגיד עתיד אבל מנביאו תדרוש ואליו תשמע וזה דעת אונקלוס שלים תהא בדחלתא דה' אלהך שלא תהיה חסר ביראתו כי "תמים" הוא השלם בדבר כמו שה תמים (שמות יב ה) שאין בו מום ושום חסרון וזו מצות עשה וכבר הזכרתי זה בפסוק והיה תמים

Rav Yehuda Oppenheimer directs us to a timely application of this idea in the Rama in OC 664:1.

הגה

כתבו הראשונים ז"ל, שיש סימן בצל הלבנה בליל הושענא רבה מה שיקרה לו או לקרוביו באותה השנה. ויש מי שכתב שאין לדקדק בזה, כדי שלא ליתרע מזליה, גם כי רבים אינם מבינים הענין על בוריו, ויותר טוב להיות תמים ולא לחקור עתידות, כן נראה לי: 

Similarly, you have the halacha in YD 179:1

אין שואלין בחוזים בכוכבים ולא בגורלות

הגה   משום שנאמר תמים תהיה עם ה' אלהיך (ב"י בשם תוספות דע"פ ובשם ספרי) וכ"ש דאסור לשאול בקוסמים ומנחשים ובמכשפים (פסקי מהרא"י סי' צ"ו

Reb Moshe, in the third Kol Rom, says like Rashi.  Reb Moshe says that even neviim are not there to tell us the future, but to give us mussar.  The Urim veTumim is to tell us whether to go to war or do something else.  But for individuals to seek to know the future is wrong.

ומ"מ התירו נביא ואורים ותומים דהנה ענין הנביא הי' בעיקר ליתן מוסר ותוכחה לכלל ישראל

and then he says

וכן כיון שיש נביא ממילא מותר לשאול אותו על דברים קטנים נמי כמו דמעשה שאול והאתונות ואע"ג דשוב אין בזה איסור מ"מ אין רוח חכמים נוחה מזה

I think that's remarkable.  You really shouldn't even ask a navi where you left your car keys.  You can, but it's not really the right thing to do.  What's wrong with seeking to know the future and trying to avoid problems?  What's' the problem?

I was discussing this with my son this morning, and I think we said a good thing, and if we're right, it's a fascinating insight.  I think pshat is that the Ribono shel Olam put us into this world not only to do mitzvos and avoid aveiros, not only for Torah, Avoda, and Gemillus Chasadim.  I think that we're alive so that we should endeavor to live complete lives.  We are supposed to learn how to be a mentsch. That means that we assess situations and decide what is best to do.  This applies in all facets of our lives, and nothing is trivial.  As the Chovos haLevavos and the Ramban say, the Torah doesn't stop at 613.  613 is just the basic blueprint, and we're supposed to build on it.  Part of that is having good manners, being efficient and useful members of society, being disciplined, and a myriad of other things that comprise being a highly functioning human being.  This is all part of Retzon Hashem, all part of lo sohu be'ra'ah, of yishuv olam, of לעבדה ולשמרה.

I think that this is not just a din in Klal Yisrael.  Every human being will be judged on whether he lived a good life, and a good life includes being a Mentsch.  All of this is part of Hashem's plan and will.  And we're supposed to learn how to accomplish these things on the basis of the information that we have b'derech hateva.  This test requires not that we get the right answer.  The Ribono shel Olam does not need us because He wants the world to run on schedule, He gave us this job so that we learn how to do it ourselves.  You might remember taking Math tests where the teacher would require not only the solution but also that you do your calculations on the test paper.  On this test you have to show your work.  We're supposed to learn how to make decisions and learn how to act on our decisions.   In a sense, doing the right thing on the basis of nevu'ah or some supernatural revelation is like insider trading.  Insider trading subverts the whole efficiency of the market.  We are obligated to learn what it means to be human, and that means to play by the rules and to learn how to function without cheating and looking at the end.

As I said, this is something my son Reb Mordechai and I were thinking about this morning.  We were trying to understand what is wrong with finding out what the future holds, what does that have to do with temimus, why can't you find out and plan accordingly.  This is our explanation.  It's hard to refrain from cheating, from trying to find out what the future holds, but Hashem tells us, "Trust Me.  This is what I want, and you should take it as it is and not seek to circumvent your obligations."
Reb Moshe's shitta on this was unique, as far as I know.  He did not encourage his family to do the Dor Yesharim test.  He did not prohibit it, but he did not encourage it.  What would he do now that almost everyone does it?  I don't know.  I assume he would say one should do it.  He didn't say you should close your eyes and cross the street.  But I don't know.

I have no mekoros for this pshat, and a vort like this really needs to stew for a long time, like bisra d'tura.  I posted it to stimulate its development.

DEVELOPMENT.
A comment came in that offered another pshat, which I think is good.  He said that Temimius means accepting that what Hashem does is good.  It is only because a person fears the future that he tries to find out what it holds and work around it to prevent disaster.  If a person trust Hashem, then he will not fear what the future will bring.  So it is davka because of temimus and faith that a person will not, and should not, seek to discern the secrets of the future.

Rabbi Dr. Richard Resnick pointed out that Rashi relates his idea of Temimus to the phrase that is found by Avraham and Noach, that they walked with Hashem.  By Noach it says  נח איש צדיק תמים היה בדרתיו את האלהים התהלך נח  and by Avraham Avinu it says התהלך לפני והיה תמים . The idea is that they walked with, they were led by, they were emissaries of the Ribono shel Olam.  They were avdei Hashem, and they did what Hashem wanted.  They did not follow Hashem out of self interest. If a person is truly an eved Hashem, and not just doing what will yield the most pleasant results to himself, he will not seek to find out and circumvent what Hashem has planned for him in the future.