And Hashem spoke unto Moses, saying:
“Speak unto the children of Israel, that they take for Me an offering; of every man whose heart makes him willing you shall take My offering.”
Shemos 25:1-2

… The building of the Mishkan had monumental significance… to create a physical structure to serve as a dwelling place of the Shechina. The Shechina is the aspect of Hashem’s presence that is openly revealed within the realm of physical creation.

… Just as the Mishkan was sanctified as the exclusive dwelling place for the Shechina, so the heart of every Jew has the capacity to become a dwelling place for the Shechina. In order to be eligible for its lofty purpose, the Mishkan needed to be sanctified; so too every Jewish person who desires to become a host for the Shechina requires a process of sanctification of the heart to be worthy of this lofty goal.

…The sanctity of space, time, and man, in which each point is intrinsically connected to the other, form a triangle of kedusha.
… Shabbos… Mishkan… and the Jewish people… are distinctive manifestations of the same reality- the presence of the Shechina.

… “Shabbos is fixed and established,” conveys the concept of sanctity of time- that Shabbos is immutable. Hashem blessed the seventh day with innate kedusha that endures and transcends the time boundaries of every generation.
In contrast to this, the kedusha of space and the kesusha of man have been altered. Prior to the sin of the Golden Calf, the entire nation was a kingdom of priests… After the sin, the rights of the priesthood were limited to the descendants of Aharon, the High Priest. [We lost part of the kedusha that only the family of Aharon kept.]

… the unconditional sanctity of Shabbos returns every week without exception. Within the pristine sanctity of the Shabbos, every Jewish soul has an opportunity to regain its own intrinsic kedusha… Shabbos is sanctified with a prohibition to engage in the mundane creative tasks normally associated with making a livelihood.

… we can build a virtual Mishkan- a dwelling place for the shechina. Shabbos has never changed, whereas we can change ourselves by opening and sanctifying our hearts to welcome G-d’s presence.

Excerpts from the the Book:

Rav Tzadok Hakohen on the Parsha – by Rabbi Yitzchak Schwartz – Mosaica Press