Musar על עירובין 3:17

This is the reason the Midrash quotes only the half of the verse which speaks about Israel building a Sanctuary for G–d, i.e. hearkening to His voice. The remaining difficulty is that since this verse speaks about the construction of the Tabernacle, why does the Torah not describe it as such and prefers to call it מקדש? We know that our sages (Eyruvin 2) have said that the terms משכן and מקדש are used interchangeably. We are nonetheless entitled to know why this is so. In view of what we have said the interchangeable nature of these two terms is now quite easily apparent. The sanctity of the people of Israel is dependent upon the construction of the Temple. When it exists, the sanctity of the pairing of G–d's uniqueness and Israel's uniqueness as symbolised by the two cherubs who face each other on the lid of the Holy Ark, and who assume a position of mutual love similar to that of man and woman, is preserved (cf. Baba Batra 99 on the significance of the positions of the cherubs). Originally, the Sanctuary was called משכן because it was only a temporary, collapsible structure. Even the so-called permanent Temple built by Solomon was still referred to as משכן, because it was subject to being destroyed sooner or later. At that time, G–d's children, Israel, were expelled from their father's table. In the future, when the Temple will be rebuilt, it will be known only as מקדש, to signify that it will be an enduring structure, never again to be destroyed.