What is "Kemo Ramim"?
Rashi #1: It is like Shamayim va'Aretz, about which two hands are said - "Af Yadi Yasdah Eretz vi'Ymini Tipchah Shamayim" (Yeshayah 48:13). Also two hands were used to make Beis ha'Mikdash - "Konenu Yadecha" (Shemos 15:17).
Rashi #2: His Mikdash is like Shamayim; He established it like the land. Just like there is no replacement for Shamayim va'Aretz, also the Mikdash has no replacement to make the Shechinah dwell there.
Radak: This is like Kemo Armonim Ramim (like tall castles). Similarly, "k'Eder ha'Ketzuvos" (Shir ha'Shirim 4:2; it should say 'k'Eder Rechelim ha'Ketzuvos'. Rechelim is omitted - Ibn Ezra there.)
Malbim: The Mikdash was a ladder standing on the ground; its top reached to Shamayim. It ties the upper world to the lower world. It is Kemo Ramim Olamos Elyonim; its foundation is like the land. The Beis ha'Mikdash and Malchus Beis David both require perfection of the Klal. Both depend on each other, like I explained below (132:11).
Why does it say "k'Eretz Yesadah l'Olam"?
Rashi: Refer to 78:69:1:1-2.
Radak: This is like it says "veha'Aretz l'Olam Omades" (Koheles 1:4). So He built the Beis ha'Mikdash there forever, unlike in Gilgal, Shilo, Nov and Giv'on. And so it says "Machon l'Shivtecha Olamim" (Melachim I, 8:13).
