Albert Barnes Commentary 1 Kings 8:10

"And it came to pass, when the priests were come out of the holy place, that the cloud filled the house of Jehovah," — 1 Kings 8:10 (ASV)

The cloud—the visible symbol of the divine presence, known as the Shechinah in the Targums—had been promised before the construction of the ark began (Exodus 29:43) and had filled the tabernacle as soon as it was completed (Exodus 40:34). It had likely been seen from time to time during the long interval for which we have no explicit mention of it.

Now, this same cloud appeared once more in full magnificence and took possession, as it were, of the building Solomon was dedicating. God's presence in the temple was thus assured to the Jews from that time forward, and His approval of all that Solomon had done was signified.