TSK · Exodus 25:17

You shall put the mercy seat on the ark of the testimony in the most holy place.

He made a mercy seat of pure gold. Its length was two and a half cubits, and a cubit and a half its breadth.

He shall take a censer full of coals of fire from off the altar before Yahweh, and two handfuls of sweet incense beaten small, and bring it within the veil:

whom God set forth to be an atoning sacrifice, through faith in his blood, for a demonstration of his righteousness through the passing over of prior sins, in God's forbearance;

and above it cherubim of glory overshadowing the mercy seat, of which things we can't speak now in detail.