28 The noun is כַּפֹּרֶת (kapporet), translated “atonement lid” or “atonement plate.” The traditional translation “mercy-seat” (so , , , ) came from Tyndale in 1530 and was also used by Luther in 1523. The noun is formed from the word “to make atonement.” The item that the Israelites should make would be more than just a lid for the ark. It would be the place where atonement was signified. The translation of “covering” is probably incorrect, for it derives from a rare use of the verb, if the same verb at all (the evidence shows “cover” is from another root with the same letters as this). The value of this place was that Yahweh sat enthroned above it, and so the ark essentially was the “footstool.” Blood was applied to the lid of the box, for that was the place of atonement (see S. R. Driver, Exodus, ).
29 After verbs of making or producing, the accusative (like “gold” here) may be used to express the material from which something is made (see §117.hh).

In other versions

“You shall make a mercy seat of pure gold. Two cubits and a half shall be its length, and a cubit and a half its breadth.

“Make an atonement cover of pure gold—two and a half cubits long and a cubit and a half wide.

Make a mercy seat of pure gold, forty-five inches long and twenty-seven inches wide.

“Then make the Ark’s cover—the place of atonement—from pure gold. It must be 45 inches long and 27 inches wide.

“And you will make an atonement cover of pure gold, two and a half cubits its length and a cubit and a half its width.

And thou shalt make a mercy seat of pure gold: two cubits and a half shall be the length thereof, and a cubit and a half the breadth thereof.

Public Domain