Albert Barnes Commentary 1 Kings 8:12

"Then spake Solomon, Jehovah hath said that he would dwell in the thick darkness." — 1 Kings 8:12 (ASV)

Rather, The Lord spoke of dwelling in the thick darkness. Solomon sees in the cloud the visible symbol of God’s presence, and accepts the token as a proof that He has taken possession of the house built for Him, and will from then on dwell there (1 Kings 8:13).