Put the mercy seat on the ark of the Testimony in the Most Holy Place.

Exodus 25:21
Set the mercy seat atop the ark, and put the Testimony that I will give you into the ark.

Exodus 40:20
Moses took the Testimony and placed it in the ark, attaching the poles to the ark; and he set the mercy seat atop the ark.

Leviticus 16:2
And the LORD said to Moses: "Tell your brother Aaron not to enter freely into the Most Holy Place behind the veil in front of the mercy seat on the ark, or else he will die, because I appear in the cloud above the mercy seat.

1 Kings 6:16
He partitioned off the twenty cubits at the rear of the temple with cedar boards from floor to ceiling to form within the temple an inner sanctuary, the Most Holy Place.

Ezekiel 41:4
Then he measured the room adjacent to the inner sanctuary to be twenty cubits long and twenty cubits wide. And he said to me, "This is the Most Holy Place."

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