Albert Barnes Commentary 1 Kings 6:20

"And within the oracle was [a space of] twenty cubits in length, and twenty cubits in breadth, and twenty cubits in the height thereof; and he overlaid it with pure gold: and he covered the altar with cedar." — 1 Kings 6:20 (ASV)

The fore part - Perhaps “the interior.”

And so covered... - Rather, “and he covered the altar of incense with cedar.” The altar was doubtless made of stone and was covered with cedar in preparation for being overlaid with gold. This overlaying was not gilding but the attachment of thin plates of gold, which had to be fastened on with small nails. This method of ornamentation was common in Babylonia, Assyria, and Media.