And you shall put the mercy seat uses the singular you and tells what to do with the completed kapporeth (see verse 17). On top of the ark is literally “upon the box down from above [it].” It should be clear that the ark has no other lid except this kapporeth.

And in the ark you shall put the testimony presents a possible problem in sequence, for the testimony should be placed inside the ark before the cover is placed on it. Note that Good News Translation and Contemporary English Version interchange the clauses to resolve this problem. The testimony, as explained at verse 16, refers to “the two stone tablets” (Good News Translation).

That I shall give you is identical with the phrase in verse 16 and does not need to be repeated. (See the comment there.)

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .