Charles Ellicott Commentary 1 Kings 6:22

"And the whole house he overlaid with gold, until all the house was finished: also the whole altar that belonged to the oracle he overlaid with gold." — 1 Kings 6:22 (ASV)

The whole altar that was by (or belonged to) the oracle. —This is the altar of incense, which, although it stood (Exodus 40:26) before the veil, and therefore in the Holy place, was considered to belong in idea rather to the Holy of Holies; since the offering of incense on it signified the approach by worship to the unseen presence of God, symbolised in the darkness and silence of the inner shrine; and the taking of the censer from it was a condition for the actual entrance into the Holy of Holies on the great Day of Atonement.

Hence in Exodus 40:5 the altar is said to be set before the ark of the testimony, and here to belong to the oracle. Probably this is the explanation of the well-known passage in the Epistle to the Hebrews (1 Kings 9:4), where the Holiest place is said to have had the altar of incense (wrongly rendered “censer” in our Authorised Version).