There are three levels: 1) השמים כסאי והארץ הדום רגלי this is explained spiritually: heaven is Torah and Neshama and earth is Mitzvos and Guf etc. 2) כי כאשר השמים החדשים והארץ החדשה אשר אני עושה when Moshiach comes there will be a real חידוש which is much more than the חידוש הישנות every second etc. in Torah, Neshama and Mitzvos and Guf. 3) כן יעמוד זרעכם ושמכם the work we did (especially in Galus) to affect this “חידוש” is forever even לעתיד לבוא unchanged.
