At the outset I'd like to point out that this term, tamim, can be translated as wholehearted or innocent, but even those concepts require us to place boundaries on what we mean. So, what does the Torah mean when it tells us to be tamim? This is not the first time we've had such an expression. When Avraham is instructed to perform circumcision he's told: Walk before Me and be tamim (Genesis 17:1). Curiously the great Bible translator, Robert Alter, renders tamim as blameless in Genesis but as wholehearted here in Deuteronomy. If I were to differ in my translations, I would have reversed them, as you'll soon see. I think that there are two varieties of perfection. In Genesis with the mitzvah of brit milah we are told to perform certain acts to achieve a more perfect state. That's the one I would have called wholehearted. This is a special form of devotion to reconstruct ourselves according to God's instructions. However, here in our parsha, we are told to be perfect by refraining from certain iniquitous behavior. I would have described that as attempting to be blameless.
What are the activities we must control to be tamim? The context is decisive. Just before the demand to be tamim the Torah tells us to avoid all types of fortune telling. The list is quite detailed. Apparently soothsaying not only was widespread but came in many flavors. Immediately after the tamim mandate we are again informed that God wants us to get rid of the guys that engage in this behavior. So, you want to be tamim, eat that fortune along with the cookie. This brings us to the crux of the matter. What's so horrendous about fortune telling and how does it diminish our perfection?
The simplest and most popular solution to this query is that we abhor fortune telling because idolaters do it. Many practices are banned in the Torah because pagans behave in that manner. Maimonides especially explained a number of mitzvoth based upon the concept of staying clear of idolatrous actions. In our case I don't think that this explanation is adequate because it doesn't enlighten us as to why this prohibition is repeated so many times and sheds no light on its connection to being tamim. Maimonides (Laws of Idolatry 11:16) gives what is for him a characteristic answer. He avers that believing these signs and portents is just stupid; it goes against scientific thinking to believe that these bizarre rituals can predict the future. To Maimonides being foolish is the worst crime of all.
I'm impressed with the position of the holy Ohr Hachyim (Rabbi Chayim Attar, 1696-1743). He suggests that there's no reason to know the future, and adjust our behavior accordingly. He points out a certain irony. One might think that knowing the future would allow a person to perfect (his word is tikun, fix) whatever might be lacking in the scenario as it unfolds. There was a television show called Early Edition that aired on CBS from 1996 until 2000. In the show an owner of a bar in Chicago got the next day's Chicago Sun-Times every morning and this allowed him to prevent a daily disaster. Rabbi Attar is informing us that such behavior is not blameless or perfect. The wholehearted or innocent behavior that we seek is not based upon foreknowledge of events. It's based upon sincere adherence to Torah principles.
We'd all love to know the results of tomorrow's races or the winning numbers for the next Mega-Amazing-Power Lottery, but that's not the way it's supposed to be. It's contrary to the ideal of human existence. Moshe wanted to know the secret of standing outside time, to know God's plan and therefore the future. He asks: If I have found favor in Your eyes then let me know Your ways (Exodus 33:13). God's answer was very clear: You shall not be able to see My face (the future), for no human can see Me and live (verse 20). Even Moshe, the greatest prophet, was severely limited in his vision of what was to be. In Hebrew the word navi or prophet has nothing to do with knowing or foretelling the future. It means relaying messages from God. Our prophets generally tell the people to be good, not what's going to happen tomorrow.
Bottom line: Don't worry about the outcome of your actions; worry about the morality of your deeds. Our definition of success is whether or not we behaved appropriately not whether we scored the most points or accumulated the most things. Life is an eternal moral challenge, not a game show with a numerical tally.
Now we can go back to the holy words of Rabbi Attar. He said that there's no reason to know the future, because we're not going to act to correct any deficient. He means that we're less interested in the outcome than in how we got there. It is about how you play the game. And we play the game according to Torah regulations which generally aren't affected by pragmatic considerations; they're affected by spiritual consequences. So go out there and play the game of life according to God's playbook. Remember focus on the rules, not the scoreboard.