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What inspired Shlomo to say this now?
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Rashi (from Mechilta Bo 12): He saw the cloud, which showed that the Shechinah dwells in the house that he built 1 - "Ki be'Anan Era'eh Al ha'Kapores" (Vayikra 16:2).
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Radak: It is because Hashem said that He will dwell among Yisrael in Arafel, i.e. a cloud - "Anan v'Arafel" (Devarim 4:11). Yonason translates ba'Arafel as 'in Yerushalayim', i.e. there He will make His cloud of glory dwell.
