The Kli Yakar, in his work Ir Giborim, speaks about the lesson from the meeting of Yaakov and Esav that we must prepare ourselves with prayer, gifts and war. He interprets our war to be the war of Torah (the disputes waged between scholars of the Torah), with which we can win over Esav. This is based on Chazal’s famous statement, “When the voice is the voice of Yaakov, the hands are not the hands of Esav” (Bereishis Rabbah 65:20). But, he says, “real war is impossible, as our Sages (Kesubos 111a) derived from the verse, I adjure you daughters of Jerusalem etc.”
In his comment on Vayikra 25:2, the Kli Yakar quotes some of the reasons given by the commentators for the mitzvah of Shmittah, rejects them, and then gives what he holds is the real reason. The Rambam in Moreh Nevuchim says that the purpose of Shmittah is to let the earth rest, so that it will produce more in the working years. The Kli Yakar argues: 1) If so, why did the Jewish people deserve exile for not keeping Shmittah? The punishment should have been the simple result of their actions: that the land would grow tired and stop producing. 2) Why is this called a "Sabbath to Hashem," if it is for the sake of the land? 3) Why does the Torah say (26:34) that during exile the land will rest and make up its missed Sabbaths? When the gentiles take over Eretz Yisroel, they will certainly not keep Shmittah, and it will not rest at all.
The Akeidah says that Shmittah is a reminder of the creation of the world. The Kli Yakar argues: For that we already have Shabbos. If a reminder every week won't help, how will a reminder once every seven years be any better?
But the true reason for Shmittah, he says, is to teach the Jewish people emunah and bitachon in Hashem. Hashem feared that upon coming into the land, working it and reaping its fruits, the Jews would begin to feel that everything was natural and they need not rely on Him. They would feel that they were the owners and masters of the land. Therefore He commanded that they work six years straight, not letting the land rest every three years, as farmers usually do, and promised that not only would the land not tire - it would produce extra in the sixth year, enough to last until the ninth year. They would rest in the seventh year, rely on miracles and know that the entire land belonged to Hashem. They would depend only on Him for their food, just as the Jews in the desert depended on Him for the manna.
The Kli Yakar's reason is really explicit in the Gemara, Sanhedrin 39a: "A student asked Rabbi Avahu: What is the reason for Shmittah? He said: The Holy One, blessed is He, said to Israel: Plant for six years and let the land rest in the seventh, so that you may know that the land is Mine."
Their failure to keep Shmittah showed that they lacked faith and felt the land was theirs, continues the Kli Yakar, and for that they were exiled. Furthermore, the Holy Land was angry at them: it had hoped to be used as a vehicle to teach the Jewish people trust in Hashem, that all Jews should know that Hashem is the true Owner of the Land, and they are mere sharecroppers. The Land, wanting to be under the ownership of Hashem alone, threw them out. During exile, the Land does not mind when gentiles live on it and farm it naturally, for the gentiles are not expected to live lives based on faith. The Land prefers this situation to the Jewish people living on it and not learning the proper lessons in emunah.
"You have circled this mountain long enough; turn yourselves northward.” (Devarim 2:2)
The Klei Yakar writes: Many say that this verse contains a penetrating lesson. It refers to both the immediate context and to future generations. Circling the mountain is a prophecy that the Jewish people will circle around, not coming close to the vineyard of Hashem Tzevaos (Eretz Yisroel). For a long time Israel will wander around it, and they will not be given even a footstep of power over it, until Hashem comes and plants His feet on the Mount of Olives.
And during all the time that Israel is wandering around, the Torah says, “Turn yourselves northward.” Tzafonah (northward) also means “hidden”; thus when it is Esav’s time to rule, we must keep a low profile. If a Jew achieves any success during exile, he should hide it from Esav, for there is no nation that is as jealous of the Jews as Esav. They consider everything we have as stolen, since Yaakov Avinu took the blessings away from Esav. And so Yaakov commanded his children, “Why do you show yourselves?” Rashi explains, “Why do you flaunt your prosperity In front of Yishmael and Esav?” In their eyes, Yitzchak stole the success of Yishmael and Yaakov stole the success of Esav. That is why this command to hide our success is written specifically regarding Esav. This is the opposite of what Jews do in our time in the lands of their enemies: any Jew who has a little money walks around in high-class garments and a beautiful house, as if he were a millionaire. With this they arouse the non-Jews against them, and transgress this verse. This is the way of most of our people, and it is the cause of all the troubles that have befallen us. Let the wise understand and learn their lesson.