Rabbi Eliyahu Dessler – Michtav Mi Eliyahu – Strive for Truth Vol 5 – Page 220
The Desert Tabernacle, the details of whose construction take up the whole of parashat Terumah and much of the succeeding parshiyot, is sometimes called sanctuary” [mikdash] (“And they shall make Me a mikdash”)(1). More frequently, however, it is called mishkan, which means “dwelling place.” (2)
The meaning of mishkan—the dwelling place (so to speak) of Hashem — is clearly expressed in the verse: “And so shall he (the Kohen Gadol) do to the Tent of Meeting which dwells with them in the midst of their defilement.”(3) God rests His presence amongst us even in the midst of our defilement because He knows that we have the ability to raise and extricate ourselves from defilement. How? Through the Torah.
The Tent of Meeting is so called because it is the meeting place of God and Israel — the place where Torah is transmitted. In parashat Tetzaveh, the Tent of Meeting is described as the place “Where I shall meet with you [plural, i.e. Israel], where I will speak to you [singular, i.e. Mosheh].”(4) “To speak to you” means to transmit Torah, and Torah learning creates a closeness be¬tween us and Hashem, a sense of joy and satisfaction. “The commands of God are straightforward and rejoice the heart.”(5) All this is included in the term mishkan.
Mikdash, on the other hand, means a place of holiness. Holiness means transcendence. We feel the absolute gulf which separates the Creator from His creatures. Our response must be service—offerings and prayer — by which we recognize our lowliness before the grandeur of the Al-mighty. “My house shall be called a house of prayer for all nations.” (6)
But nevertheless, we find that mishkan is sometimes called mikdash and mkdash is sometimes called mishkan.(7) How they are called reflects what they are in reality, for their meaning and existence are really one. If mishkan represents the joy in the presence of Hashem, and mikdash represents the awe one feels in the transcendence of Hashem, then together they form one whole. We have to “rejoice in trembling.”(8) And the Rabbis say: “I experience fear in the midst of my joy and joy in the midst of my fear.” (9)
1 Shemot 25:8.
2 Ibid. 25:9.
3 Vayikra 16:16.
4 Shemot 29:42.
5 Tehillim 19:9.
6 Yesha’ya 56:7.
7 Eruvin 2a.
8 Tehillim 2:11.
9 Tanna de-Be Eliyahu Rabba #3.