What is "Beis Zevul"?
'Rashi': It is a dwelling.
Why did he say that Hashem will dwell in it forever?
'Rashi': Once it was chosen, the Shechinah did not dwell elsewhere, and Bamos were not permitted. Radak ? Shilo, Nov and Giv'on were not permanent, for they were not "ha'Makom Asher Yivchar Hashem" (Devarim 12:5). Only here, Har ha'Moriyah, the place of Akeidas Yitzchak, about which it says "Hashem Yir'eh? b'Har Hashem Yera'eh" (Bereishis 22:14) ? Hashem will appear there for all generations 1 . When David saw that he was answered there "va'Ya'anehu va'Esh Min ha'Shamayim", he know that it is the place that Hashem chose, and said "Zeh Hu Beis Hashem" (Divrei ha'Yamim I, 21:26, 22:1).
Malbim (Melachim I, 8:13): Hashem already dwelled here when it was Tohu va'Vohu (empty), darkness, cloud, a mountain, field and granary. Now that I built a house for You, I know that it will be Your permanent primary dwelling. Your dwelling in upper worlds will be via the Mikdash. The light will illuminate from the Mikdash to all the worlds.
Malbim (Melachim I, 8:13): It is also where Yitzchak went "Lasu'ach ba'Sadeh" (Bereishis 24:63, i.e. to pray), and where Yakov saw the ladder when he left Charan (refer to Bereishis 28:10:3:2), and where the Shechinah appeared to David.
