The first question that one asks when learning Parshat Behar - the first question of Rashi - is why is it that the commandment of Shmittah is juxtaposed with 'Behar Sinai'? Why is that shmittah specifically was chosen to be said to be given at Har Sinai. Rashi answers that it is so we know that just as the mitzvah of Shmittah in all its detail was given at Sinai, so too, all the mitzvot were given in all their detail as well. Why use shmittah then? One might say that it is because at that time Shmittah was the least relevant since the first shmittah year was not to be for another 7 years that then turned into 47 years, however, the previous Lubavitcher Rebbe T"ZL writes in Likutei Sichot that if this were the reason, then why was the mitzvah of Hakhel not chosen in which Am Yisrael are commanded that on the Succot after the Shmittah year, the Am gathers in the mikdash and the King reads the Torah, surely this occurs even after shmittah? The Rebbe answers that Shmittah is a mitzvah that is based in agriculture and that these mitzvot are of the greatest importance too.
The Netivot Shalom furthers the question. He quotes the Mishnah in Avot that says that Galut is brought on through four sins, Avodah Zarah, promiscuity, murder and not keeping Shmittah - why is it that shmittah is seen as such an important to mitzvah. Unfortunately, most of us still live in Chutz La'aretz where shmittah is barely relevant to us on a day to day basis, what is the reason that it is so important? The final question he brings is on the phrasing of the first Mishnah in Avot which says - 'Moshe kibel Torah MiSinai etc.' - why does it say Moshe received the Torah FROM Sinai? Didn't he receive the Torah from HaShem, the rest of the Mesorah in the Mishnah is between beings so why does it not say Moshe kibel Torah M'HaKadosh Baruch Hu?
The reason we do or do not do a mitzvah, the Slonimer Rebbe explains, is because of emunah, it is a foundation of every mitzvah - the Rambam rights that the commandment of 'Anochi HaShem...' is the mitzvah of Emunah! The preparation for receiving the Torah at Har Sinai was the experience in itself of Maamad Har Sinai - the greatest revelation of G-d's power in history - how could a person experience it and not have Emunah in HaShem. This is one explanation of the famous Gemara that said that G-d held a mountain of Am Yisrael's head until they said 'Na'aseh V'Nishmah' - who wouldn't say Na'aseh V'Nishmah if they experienced Ma'amad Har Sinai says the Meshech Chochma.
There are different levels of Emunah as previously mentioned, Emunah of the mind that understands and believes in G-d, emunah of the heart (lev) and emotions and emunah of the limbs (eivarim) that puts it all into practice. There is obviously a difference between saying that one believes in G-d and even feeling it in their hard and actually putting it into practice, making avodat HaShem like reflex of one's limbs. This is the highest level of emunah that Am Yisrael reached at Har Sinai - the Na'aseh of Na'aseh V'Nishmah.
The root of every mitzvah is Emunah. One needs to have their general Emunah in G-d's constant hashgacha in the world and also Emunah in the reason for every mitzvah. Shmittah is the only mitzvah in the Torah that reflects on a national level the Na'aseh V'Nishmah of Ma'amad Har Sinai. Shmittah is not just Emunah of the Lev - it is completely Emunah of the Eivarim - a person stops working for a year, not knowing where their food is going to come from, not knowing where their income is going to come from - it is voluntary unemployment but having complete Emunah in HaShem to provide. It is a mitzvah for the whole of Am Yisrael - either everyone does it or noone does it since if one person chooses not to do it, they will make all the money and this will lead to other people also doing it in competition - it has to be done by the whole of Klal Yisrael! It is also the highest notion of a mitzvah where all the details have to be kept since all the mitzvot of Shmittah have to be kept precisely.
Returning to our original question - why is Shmittah and all its details specifically said to have been said at Har Sinai? The Netivot Shalom answers that it is to teach us that in the same way Shmittah requires a full Emunat Eivarim, we should also put into every mitzvah also taught at Har Sinai - ALL MITZVOT - the same Emunah Eivarim and make avodat HaShem a reflex built into us. Without Emunah we do not deserve to be in Eretz Yisrael this is true from the case of the ma'apilim who attempted to enter the land at the time of the meraglim and were not on the madreigah to live in Israel and were killed before they could enter the land, right through to today - it is not an easy time to live in Eretz Yisrael and its easy to find all the excuses in the world not to fulfill HaShem's mitvot but if we have full Emunah in HaShem we will all be zocher to live in Eretz Yisrael and fulfill all of HaShem's mitzvot to the highest extent. This is especially relevant this year as we celebrate sixty years of Medinat Yisrael and even more so the Shnat Ha'Shviit itself! May we soon see a complete redemption for the whole of Am Yisrael.
