Daled Minim
Small to Man, Big to Hashem:
The pasuk states (Mishlei 30:29): "Three are outstanding in their step, and four are outstanding in their walk." The Medrash (Vayikroh Rabbah 30:14) says that this refers to the Daled Minim. Every Jew runs to acquire the finest minim in order to glorify Hashem. It states: "They appear small to human eyes, but they are big to Hashem."
Like Fulfilling All the Mitzvos:
The Yesod V'Shoresh Ha'avodah (Shaar 11, Perek 14) quotes a Medrash that says that one who takes the four minim is considered like he did all the mitzvos. The Avudraham adds that the gematriah of “esrog im gimmel minim" is 613.
The Joy of Fulfilling a Mitzvah L'Shem Shomayim:
There once was a shortage of esrogim. A man came to the Vilna Gaon zy"a and told him that he was willing to give him his esrog on one condition – that he would receive all the reward for the mitzvah.
The Gaon said, "This is a really good deal. It would even be worth it for me to give away my entire portion in Olam Haba for the chance to perform the mitzvah of esrog properly."
When he was handed the esrog, the Gaon was full of joy. He declared, "This year I have the zechus to do a mitzvah 100% l'sheim shomayim, with no personal considerations!"
Selling a Horse for an Esrog:
Sefer Zichron Tzadikim (Chelek Hei) relates that Rav Nachman of Radvill zy'a (brother-in-law of the Magid of Zlotchov zy"a) once went to the city of Lemberg to purchase an esrog mehudar. He brought along with him a lot of money for this purpose, and traveled in his horse and carriage, along with his attendants. When he got to Lemberg, he saw that the price of esrogim had gone up substantially. He didn't have enough money to buy a nice one. Therefore, he sold his horse and carriage in order to purchase a good esrog, and he hired a wagon driver to take him home.
A Revelation Through the Daled Minim:
Sefer Zichron Tzadikim (Chelek Aleph, Erech Rav Pinchos of Koretz, Siman 14) relates that before his greatness was revealed to the world, Rav Pinchos of Koretz zy"a was a very poor man. He would sit all day in the bais medrash, immersed in his holy avodah. Although he and his family were starving, he accepted it all with love. Since he was unknown to the public, no one offered to support him.
One year, the esrog crop was inferior in quality, and almost no kosher esrogim could be found. When Rav Pinchos heard people talking about the problem in the bais medrash, he said with his ruach hakodesh, "I will, im yirtzah Hashem, have a kosher esrog."
The people who heard him say this laughed at him. They wondered how a poor batlan could possibly get a good esrog when even the wealthiest men couldn't get their hands on one. However, he insisted that he would have a kosher esrog for Yomtov, and the men continued to mock him.
Erev Sukkos arrived, and there still were no kosher esrogim in town. On Sukkos morning, someone asked him, "Do you still believe that you'll have an esrog?"
He answered, "The k'hal still hasn't reached Tefillas Hallel!"
Again, he was laughed at and told he was dreaming.
Everyone was shocked when the chazan finished Chazaras HaShas of Shacharis, and a gentile rode up to the shul on a horse, with a beautiful esrog in his hand, as well as the other three minim, already tied up nicely in accordance with halacha. He gave the Daled Minim to Rav Pinchos, who made a joyful, enthusiastic blessing on them.
It was later learned that during the summer, Rav Pinchos had met a friend of his who lived in the city of Zeslov. This man was a merchant who traveled far and wide for business. Rav Pinchos told him, "When you get to a place where esrogim grow, please buy a nice one for me."
There was still a long time until Sukkos, and the merchant wondered why Rav Pinchos was thinking about esrogim, but he did as he was asked. He bought an esrog as soon as he could and kept it in his home until erev Sukkos.
Since he couldn't travel to Koretz himself, he hired a non-Jew to take it for him, and the messenger arrived on Sukkos morning, right before Hallel.
It then became known that Rav Pinchos was a holy man who could see things that others could not.
Pri Eitz Hadar-Horse:
Rav Mordechai of Neshchiz zy"a lived a difficult life. He was so poor that all he ever ate during the week was bread with salt. On Shabbos, he would also have a bit of herring. All year long, he would put away a few pennies each week to save enough to buy an esrog mehudar for Sukkos.
One year, he traveled during the days between Rosh Hashanah and Yom Kippur to the city of Brody to purchase an esrog. He had with him 10 rubles, which he had managed to save up over the course of an entire year. On the way, he met a Jew who was crying bitterly. Rav Mordechai asked him why he was weeping, and the man said, "I have been struck with a terrible tragedy. I live in a nearby village, where I make my living as a water carrier. I have a horse and wagon and a barrel that I fill with water from a well in a field. I make just enough money to live very simply. Today, my horse collapsed and died. I don't have any money for yomtov, and I cannot afford to buy a new horse!"
Rav Mordechai immediately took out his ten rubles from his pocket and gave them to the water carrier, saying, "Use this to buy a new horse."
He came home empty-handed, without any money and with no esrog. When he got home, he happily told his chasidim, “Boruch Hashem, Hashem sent me a 'pri eitz hadar' for Sukkos. Everyone else will make a bracha on an esrog, but this year I will make a bracha on a horse!"
Zerizin Makdimin L'Mitzvos:
There once was a severe shortage of esrogim, and only one esrog could be procured for the entire city of Berditchov. The esrog was kept in the home of Rav Levi Yitzchok zy"a, and everyone came to his house to make a bracha on it. The shamash thought to himself: After Rebbe makes a bracha on the esrog, the next in line will be the distinguished scholars and leading chasidim. After them will be the turn of the wealthy men. By the time I get a turn, it will be almost nightfall. Why should I have to wait so long? Why am I worse than them?
He decided that early in the morning, when the Rebbe went to the mikvah, he would stealthily take the esrog and make a bracha on it.
That's exactly what he did. He got up early, waited for the Rebbe to go to the mikvah, took out the esrog, and made a bracha. However, since he was so scared that someone might see him, he began to tremble. The esrog fell to the ground, and the pitom fell off, rendering it posul.
The shamash was overcome with grief and fear. When Rav Levi Yitzchok returned, he tearfully told him what had happened. He thought the tzadik would be angry with him, but he was amazed to see that he remained fully calm. He held the esrog in his hands and emotionally declared, “Ribono Shel Olam, look at how much Your children love mitzvos. This man wanted to do the mitzvah of Daled Minim with zerizus. He put so much effort and even placed himself in danger of being yelled at so that he could be amongst those who are zerizin makdimin l'mitzvos.”
An Esrog Like a Heart:
The Ropshitzer Rebbe zy"a would say that the reason we make sure that an esrog has no blemish at all is that an esrog is comparable to the heart, and even a tiny blemish on the heart is very dangerous.