http://revach.net/article.php?id=3553

Section: Parshas HaShavua   Category: Quick Vort
Parshas Pikudei: The Bais HaMikdash Could Have Lasted Forever
"Eileh Pikudei Hamishkan Mishkan HaEidus Asher Pukad Al Pi Moshe" (Pikudei  38:21).  These are the accounts of the Mishkan, the Mishkan HaEidus, that were accounted for on the word of Moshe.  Rashi says that the word Mishkan is like Mashkon, a guarantee.  When Klal Yisroel sinned, Hashem took away the Bais HaMikdash as collateral instead of destroying Am Yisroel.  That is why it says the word Mishkan two times, for the first and second Bais HaMikdash that were ultimately destroyed.

Rav Shimon Sofer in Shir Ma'on says that this fits in nicely with the rest of the pasuk.  We know that if Moshe would have gone into Eretz Yisroel, the Bais HaMikdash would never have been destroyed.  The word Pakad also means "missing" or "lacking".  "Eileh Pikudei Hamishkan", this is why the Bais HaMikdash is missing.  "Al Pi Moshe", because Moshe erred with his mouth by saying Shimu Na HaMorim as he hit the rock instead of talking to it.  He then lost his right to go to Eretz Yisroel and the Bais HaMikdash did not last forever.