In the Mishna on the Omud Aleph it tells us that the Bnei HaMedina would only take the 4 MINIM round 1 day and then Rav Yoichonon Ben Zakai was goizer as a Zecher for the Mikdosh to take 4 MINIM 7 days. But I am completely misunderstanding something but isnt this a geder of "Chotey Nizkar" You Bnei Medina before the churban and there was a Beis Hamikdosh around you were ONLY able to take the 4 MINIM 1 day, but the good news is now that we are all upset that the churban happened and the Beish Hamikdosh is no longer around you Bnei Medina are being "rewarded" with a "zecher" that you are now able to take the 4 MINIM for 7 days. Hayitochen !! Sorry, to me it does not add up. Look at what did Reb Yoichonon Ben Zakai "Tu Oif" for the Bnei Medina he has given them more sechar and opportunity to be mekayem Mitzvos 4 Minim AFTER the Churban than BEFORE!!!
Boruch Kahan
1) It is like fasting on Tish'ah b'Av. We get Sechar for fasting on Tish'ah b'Av. We would rather have the Beis ha'Mikdash and not have to fast, but we get rewarded for remembering it. We lost the opportunity to fulfill a lot of Mitzvos when we lost the Beis ha'Mikdash, but ha'Kadosh Baruch Hu did us a Chesed by giving us some Mitzvos which help us remember it.
2) We get rewarded for waiting for the Beis ha'Mikdash:
The Gemara in Sanhedrin 97b asks, "Why are we waiting for the Mashi'ach?" The Gemara answers that we wait in order to receive reward: "Ashrei Kol Chochei Lo."
When shake the Lulav all seven days of Sukos, we get a Sechar for remembering the Beis ha'Mikdash and waiting for it to be rebuilt.
3) Reb Borucb, I think there may be a Nafka Mina l'Halachah from your question. I will explain bs'd.
The Halichos Shlomo (month of Tishrei, chapter 11, Din 25, p. 234) writes in the name of Rav Shlomo Zalman Auerbach zt'l that since holding the Lulav on the days other than the first day of Sukos is in order to remember the Beis ha'Mikdash, it is correct to have this Kavanah in mind when doing the Mitzvah.
In note 41 at the bottom of the page there they write in his name that since in Sukah 41a it is stated that the reason for holding the Lulav all seven days outside the Beis ha'Mikdash is because of the verse, "That is Tziyon whom no one seeks out," from which we learn that one should seek out Tziyon, it is logical that wben one holds the Lulav he should have this Kavanah in mind, since the entire Takanah was in order to remember the Beis ha'Mikdash.
Further down the page, in note 113, they cite Rav Shlomo Zalman that one should teach this Halachah inside one's home (to his family).
Of course, the Gemara in Sukah 41a about seeking out Tziyon also appears here in Rosh Hashanah 30a.
Reb Boruch, I think that one of the reasons why Rav Shlomo Zalman might have said this Chidush is to answer your question -- namely, why, after the destruction of the Beis ha'Mikdash, do we have seven happy days of holding the Lulav and Esrog outside the Mikdash, but when the Beis ha'Mikdash was standing we had only one day of holding the Lulav outside the Beis ha'Mikdash?
The answer is that the Takanah was not made specifically in order to make us happy. The Takanah was made in order to remember the Beis ha'Mikdash. If it also makes us happy, there is nothing wrong with that, but that is not the main reason and one should keep the main reason in mind.
Dovid Bloom