Cross reference
Exodus 26:34
34 You shall put the mercy seat on the ark of the testimony in the most holy place.
Exodus 25:21
21 You shall put the mercy seat on top of the ark, and in the ark you shall put the testimony that I will give you.
Exodus 40:20
20 He took and put the testimony into the ark, and set the poles on the ark, and put the mercy seat above on the ark.
Hebrews 9:5
5 and above it cherubim of glory overshadowing the mercy seat, of which things we can't now speak in detail.