The Mishna on Amud Beis quotes a verse that describes the (Paroches) separation between the sanctuary and the Holy of Holies. The verse is reminiscent of a similar verse in Bereishis that describes the firmament that separates between the upper waters and lower waters. Numerous commentaries noted the similarities of the verses from the Mishkan and the creation verses in Bereishis, and see mystical implications.

The Shalah (Torah Shebikhtav, Terumah, Torah Ohr) gives an in depth explanation of the function of the Mishkan/Beis HaMikdash, of which I will try to say over certain highlights. 

The Mishkan and the Beis HaMikdash were a representation of the entire creation, physical and spiritual pleroma. The Midrash tries to explain the value of this effort to recreate this structure with the following parable:

A king once appeared to his subjects in a bejeweled cloak. They admired it and the king asked that they make their own cloak for him that he can wear when he visits. The subjects said, “Do you believe that we have access to the wealth and ability to make a jeweled cloak like the one you have?“ The king answered, “you do it with what you have, and I will appreciate it for what it is.“ 

The parable on a simple level is indicating that though we cannot really create a place for God‘s presence to reside in any manner that is fitting or appropriate, God accepts our effort to do so with the tools we have at hand. 

Here are some of the scriptural parallels between the Bais HaMikdash and the heavenly and earthly structures:

Psalms 104:2 refers to heavens as "You spread the heavens like a tent cloth", while the Mishkan also is covered by tent cloth. When describing what happened on the second day of creation, the Torah speaks about a firmament which is to separate the "upper" waters from the "lower" waters (Genesis 1,6), whereas when giving the instructions for building the Mishkan the Torah directs that the "curtain shall divide between the Sanctuary and the Holy of Holies" (Shemos 26:33). The Torah, relating the work G–d performed on the third day of creation, mentions that the waters are to be gathered into one area (Bereishis 1:9), whereas during the construction of the Mishkan the Torah commands the construction of a copper basin into which all the water is to be poured (Shemos 30:18). On the fourth day of creation the Torah reports the construction of the Sun, Moon and Stars (Bereshis 1:14), whereas the Torah commands the construction of a Menorah.  

The Shalah goes on to list many more correspondences between the heavenly sphere and the Mishkan.  The key point is the correspondence. However, the question is, to what end and ultimate purpose is this for?

To understand this, one must understand a basic mystical concept that is expressed consistently but in a variety of ways. One way that it is expressed is that upper worlds need an awakening from the lower worlds in order to bring a divine flow and blessing. It is known as the

 זהר ח''ג צ''ב באתערותא דלתתא אתערותא דלעילא

This idea is everywhere in Judaism. As just one example, saying Kedusha down here on earth enables the angels to recite Kedusha in Heaven (Nefesh HaChayyim Gate I:6). The belief that God needs us to need Him in order to draw His blessings is fundamental in Judaism. The structure of the Mishkan and Beis HaMikdash was designed to create a meditative awareness of the Heavenly world and its connections to our world by virtue of its symbolic construction.

The Shalah adds another dimension to this. Witnessing the detailed and elaborate construction of the Mishkan also lends an appreciation to the elaborate construction and creation of the universe. Kind of when you make a small replica of something such as a ship in a bottle as an homage to the actual item. In addition, the idea that the Mishkan was built out of voluntary contributions emphasizes the importance of the internal non-coercive realizations that allow us to bring God’s blessings into this world. 

I will conclude with an observation. One might wonder about the ultimate function of the Paroches. Why was it even necessary to have a curtain separating between the Holy Holies in the sanctuary? Would it not be enough to just build that particular space as sacred? This brings us to the idea that Humans will always need symbols to represent their thoughts, truths and emotional processes. The Mishkan and its separate domains, the way it represents the heavenly spiritual domain and its relationship with the physical world are important. We must understand and accept it for what it is.  

We all need boundaries to have a good relationship.  And, even to have a good relationship with God, we need boundaries.