While in exile after the destruction of the first Beis Hamikdash, Hashem told the prophet Yechezkel to teach the Jewish people the details of the design of the Beis Hamikdash.
Yechezkel challenged Hashem, “how are they capable of making the Beis Hamikdash while they are in exile? First let them leave their exile and then I will tell them!”
Hashem responded “just because My children are in exile should the construction of My home be neglected?... Let them involve themselves in learning about the structure of the Beis Hamikdash, and I will consider it as if they are involved in building it.”
The mystics and Jewish philosophers understood that the design of the Beis Hamikdash parallels the soul and contains within it lessons on how we are to serve Hashem, so that His presence can rest within us and we become a Mishkan for His presence.
The integrity of the physical structure of the Beis Hamikdash is dependent on the integrity of the spiritual Beis Hamikdash in the souls and service of the Jewish people.
The Jewish people were in exile because of their sins and the destruction of their inner spiritual “temples”. This resulted in the destruction of the physical Temple.
Hashem instructed Yechezkel to teach the Jewish people the details of the Beis Hamikdash, so that they could reflect on the lessons hidden within its design and rebuild their own temples, paving the way for the restoration of the physical structure as well.
The Three Weeks, when we mourn for the destruction of the Beis Hamikdash is an appropriate time to study about the Beis Hamikdash and become partners in its rebuilding.
