Our Parsha opens with the Pesukim that detail the famous warning that Hashem gives to Bnai Yisrael. The Torah begins by stating "אם בחקתי תלכו ואת מצותי תשמרו ועשיתם אותם," "if you will walk in (accordance with) my decrees and observe my laws and perform them" (ויקרא כ"ו:ג'). The next Posuk starts with the word ונתתי"," which is commonly translated as "then I will give" )שם פסוק ד'(. Using this translation, we are prone to view the Posuk as setting up a classical warning. If we follow the laws, then we will be beneficiaries of all the lavish rewards in the Parsha. Rains will fall at the proper times, the land and trees will produce abundantly, and we will live securely and peacefully. However, if we do not follow these laws and we reject them (שם פסוק ט"ו), then we call Hashem's wrath upon ourselves. We will be subjected to terrible sickness, famine and loneliness. Our rejection of Hashem's Torah will cause us to be rejected by the world and its elements. To translate "ונתתי" as "then I will give" makes this appear as a warning in the conditional sense. If you do this, then I will do that, and if you don't do this, then I won't do that.
The Mishnah in Kiddushin (פרק ג' משנה ד'), understands this to be a תנאי כפול, a "double" or "folded" condition. This "double" or "folded" quality is shown by having the condition stated in both the positive and in the negative. The requirement that conditions be stated in the positive and negative is quoted in the name of Rabbi Meir. Rabbi Meir proves this point from a Posuk later in the Torah (במדבר ל"ב:כ"ט) where Moshe uses such a תנאי כפול when speaking to the tribes of Gad and Reuven. In that Mishnah )שם(, Rabbi Chananya says, however, that Moshe didn't mean for this to be the prototype for all conditions; rather Moshe needed to state the condition in the negative so as to eliminate a possible confusion which might have resulted had he not stated it this way. Rabbi Chananya would then be saying that the תנאי כפול of Moshe is not an example of the rule, but an exception to the rule. Would our Parsha prove to be a difficulty for Rabbi Chananya in that Hashem himself apparently uses a תנאי כפול? Probably not, in light of the Mishnah that follows (שם משנה ה'), which says that if someone engages a woman on the condition that he converts to Judaism, the engagement is not valid. This can be understood to teach us that conditions that are absolute prerequisites for any event to take effect are not valid conditions, meaning that one can not impose a condition which is necessary anyway for the fulfillment of an event. In this case, there is no choice but to have the betrothal only after the conversion, because before one's conversion, his act of betrothal in its Halachic sense is meaningless. For a condition to be effective, the person stating the condition must have the choice himself of invoking it or not. The Ramban on our Parsha (ויקרא כ"ו:י"א) says that the Torah here shows us that when Klal Yisrael obeys Hashem, their existence is not governed by the natural order of things, but by divine intervention. The consequences of the "condition" in our Parsha would then be a type of reward and punishment. This would represent another exception to the rule for Rabbi Chananya because just as Hashem is in control of the world and nature, something we have no control over, so too His conditions are different than ours and we cannot infer practical laws for human beings from them. Therefore, one can not prove anything about תנאי כפול from our Parsha, since it is not a standard type of condition, because there is nothing over which Hashem has no control, unlike human beings.
However, if one were to translate the warning of "ונתתי" as "and I will give," as opposed to "then," we see a stark difference. The results of the warning would be natural consequences as opposed to rewards and punishments. If one is ill and avoids medicine, remaining ill is not a punishment, it is a natural consequence. This idea would be in harmony with what we are taught in Pirkei Avos )פרק א' משנה ג'( that one should not serve Hashem "על מנת לקבל פרס," "on the condition of receiving reward." The benefit of doing Mitzvos is not a reward, because in this world, the benefit of Mitzvos is within the natural order of things. True reward is reserved for the world to come. Our Parsha would thus not be presenting a condition for rewards and punishments to take effect, but rather stating the natural consequences of the observance of Mitzvos or of the failure to observe them.
Regardless of how one perceives the consequences of the performance of Mitzvos, however, whether as natural or as extraordinary, there is a serious danger involved here. In our day to day lives, we may fall prey to taking this warning as a kind of business deal. It is as if we are being told: Follow the rules or don't follow the rules - with no emotion involved at all! The deal apparently will work either way. Follow the laws and prosper, or, conversely, reject them and suffer. But this is not the proper approach; there must be passion and emotion involved with Mitzvos.
As we approach the Yom Tov of Shavuos and prepare ourselves for the receiving of the Torah, we must imbue ourselves with a zest and passion for learning. In essence, this is why Rashi comments on the beginning of our Parsha (שם פסוק ג') that the word "תלכו," " you will walk," tells us to be עמלים בתורה, diligent, hard workers in Torah. Rashi is cautioning us to avoid observance in a perfunctory way. We must labor arduously in pursuit of Torah. Similarly later on when the Torah tells us that "these are the laws which Hashem gave between Himself and Bnai Yisrael" (שם פסוק מ"ו), the Torah uses the term "תורות," in the plural, to describe the laws. What two Torahs are there? Rashi )שם( says that this refers to תורה שבכתב and תורה שבעל פה, the written and the oral law. Both were given to Moshe at Har Sinai. These are the areas in which we should toil. With Hashem's help, may we all experience a Shavuos where we do more than accept the Torah passively, but open our hearts to allow Hashem's will to identify and merge with our own.