"Hashem's portion is His people; Yaakov is the measure of His inheritance - Yaakov chevel nachalaso (Ha'azinu 32:9)." Why does the Torah use the word chevel to describe how the Jewish people are Hashem's special portion? And why is the name Yaakov chosen to identify Klal Yisrael in this context?
Rav Yaakov Kamenetsky (Emes L'Yaakov, Bamidbar 1:1) points out that each shevet in Klal Yisrael had a unique mission in avodas Hashem. This was symbolized by the fact that each shevet had its own stone on the breastplate of the Kohen Gadol and its own flag. Once the Mishkan was built and all of Klal Yisrael had one central location to focus its spiritual energies, there was no longer a concern that the individuality of each of the shevatim would lead to divisiveness and confusion. To the contrary, by uniting under the banner of Torah and mitzvos, the different shevatim would be able to use their individual strengths and unique spiritual talents to serve Hashem, and this multi-colored, variegated avodas Hashem would actually add to and enhance k'vod Shamayim.
A similar idea is alluded to in a statement of Chazal. The Gemara (Sukka 53a) says that when Hillel would rejoice at the Simchas Beis HaShoei'va in the Beis HaMikdash, he would say, "If I (ani) am here, then all is here, and if I am not here, then who is here?" Why would Hillel make a statement that sounds arrogant? Rashi explains that when using the word ani, Hillel was actually speaking on behalf of Hakadosh Boruch Hu. What he meant to say is that it's as if Hashem is constantly telling us, "If you do not sin, My presence will rest on the Beis HaMikdash and everyone will come here; but if you do not behave properly then I will leave the Beis HaMikdash, and no one will come here."
Tosafos quotes a different interpretation in the name of the Yerushalmi, that Hillel's ani did not refer to Hakadosh Boruch Hu, but rather to Klal Yisrael. Hillel meant to underscore the value of Klal Yisrael, that when Klal Yisrael is serving Hashem in the Beis HaMikdash, all is there. But if Klal Yisrael is not there, then there is no value to whomever is there.
What is the deeper message of Hillel's statement? Why did he specifically use the word ani to refer to Klal Yisrael? Perhaps what Hillel meant to say is, "If I am realizing my full spiritual potential, then everything (my real essence) is here; but if I am not focusing my energies on becoming the person that I am meant to be, then who is here?" Hillel was hinting to the fact that every member of Klal Yisrael has a special spiritual mission that no one else can fulfill. As he says elsewhere (Avos 1:14), "If I will not be for myself, then who will be for me?" If I will not accomplish my purpose in life, no one else can do it for me. Every Jew has a unique role to play in this world, and the ultimate shleimus of Klal Yisrael is reached only when each individual Jew lives up to his full potential, his ani. This produces the greatest k'vod Shamayim - when Hashem rests His Presence on the Beis HaMikdash in the fullest sense and "all is here".
But this idea goes even further. The halacha is that although one is not obligated to bind the lulav with the hadassim and aravos, nevertheless, in order to beautify the mitzvah, it is appropriate to do so (Shulchan Aruch, Orach Chaim 651:1). What's more, when shaking the four species, one is obligated to hold the esrog close to the other three species (ibid 651:11). The Biur HaGra explains that the source of this halacha is the Midrash Rabbah (Emor 30:11) that Klal Yisrael is composed of four types of people: those who are involved in Torah and ma'asim tovim, those who have only Torah, those who have only ma'asim tovim, and those who have neither. Hakadosh Boruch Hu says, "Join them together, and they will atone for each other, and...I will be elevated."
The Beis Yosef (ibid) cites a different source for this custom in the name of Rav Menachem Rikanti. Apparently, one time, on the first night of Sukkos, the Rikanti had a guest. In the middle of the night, the Rikanti saw in a dream that the guest was writing Hashem's name, but he was separating the last letter from the first three. The Rikanti criticized his guest in the dream, and he fixed Hashem's name so that all the letters were close together. But he could not understand the deeper meaning of the dream. The next day he saw that his guest shook the lulav, hadassim and aravos without the esrog. And then he realized that the four species symbolize Hashem's name, as it says in the Midrash Rabbah (Emor 30:9), so if one does not join all the species together while shaking them, it is like he is separating between the letters of Hashem's name.
There seems to be a contradiction in the words of the Midrash. Do the four species correspond to the four groups of Jews or to the four letters of Hashem's name? The answer is that they correspond to both, because it is through Klal Yisrael that Hashem's name and the values of the Torah are promoted throughout the world. The shaking of the four species teaches the importance of uniting together with other Jews - with those who have Torah or ma'asim tovim, and even with those who have neither Torah nor ma'asim tovim. When we appreciate the value of all types of Jews, and we show concern even for those who are spiritually lost, we connect the letters of Hashem's name and we bring honor to the Torah and its ideals.
Perhaps this is why the Torah describes the Jewish people as "Yaakov chevel nachalaso". Unlike Avraham and Yitzchak who transmitted their Torah tradition to only one of their children, Yaakov Avinu had twelve shevatim, and one of the lessons he taught them is that each shevet in Klal Yisrael has a unique role to play in avodas Hashem, and Hashem values the individual contributions of each shevet and each member of Klal Yisrael. A chevel, a rope, is braided from different strands. When all of the strands are joined together, the rope becomes stronger and it is able to withstand even powerful external forces that are exerted upon it. Similarly, when Klal Yisrael is united under the banner of Torah and mitzvos, the special avodas Hashem of each individual Jew - whether in Talmud Torah, or tefillah or chessed - makes Klal Yisrael as a whole even stronger, and serves to increase k'vod Shamayim in the world.