Don't buy a lemon... buy an esrog!
The esrog is said to represent the heart (because of its shape), and also said to represent the ideal kind of Jews, who have both knowledge of Torah and good deeds (because it has both a pleasant scent and a pleasant taste). The ancient Greeks called the esrog fruit the Persian apple, Median apple or golden apple – and according to one midrash, it was the fruit eaten by Adam and Chava for which they were expelled from Gan Eden.
However, when it comes to the mitzvah of Arba’as HaMinim, how do we know that we must take specifically an esrog rather than just any old fruit such as a lemon or an orange?
In Sefer Vayikra (23:40) the passuk states that one of the Arba’as HaMinim should be “pri etz hadar - fruit of a tree which is hadar.” The common meaning of “hadar” is “beautiful”, however we have a tradition from the times of Moshe Rabbeinu that this fruit is in fact an esrog.
The Ramban writes in his commentary on the passuk, that hadar is simply the ancient Hebrew name that refers to an esrog (which is the Aramaic term for the fruit). In other words, the Torah is simply instructing to take the “fruit of a tree which is an esrog”.
The Ibn Ezra explains that the mitzvah is literally to take the most beautiful of all fruits, which in the opinion of the Ibn Ezra is specifically an esrog.
The Rabbanim in the Gemara (Sukkah 35a) learn out from the words “fruit of a tree,” that the mitzvah requires a tree which tastes similar to its fruit, and the wood of the esrog tree has a similar taste to its fruit.
Rabbi Yehudah HaNassi, in the Gemara, explains that “hadar” can also be read “hadir - a sheep pen”, from which he learns that just as a sheep pen contains both old and young animals, so too, the tree must simultaneously hold both old and young fruit. As the esrog trees grows fruit throughout the year, it may simultaneously hold both old and young fruits. Rabbi Abahu suggests an alternative explanation, wherein the word “hadar” is translated to mean “the one that resides” – a reference to an esrog’s lengthy growth and ripening term. Ben Azzai suggests a further alternative. He says that “hadar” has the same root as the Greek word “hydor – water”, referring to the fact that the esrog tree requires more hydration than other trees.
There is also a famous teaching of the Rebbe Rashab in the name of the Alter Rebbe of Chabad that when Hashem told Moshe Rebbeinu about the mitzvah of Arba'as HaMinim they sent messengers on clouds to bring back specifically Calabrian esrogim. To read more about Calabrian esrogim click here.