Isaiah 51:15 (King James Bible) but I am the LORD thy God that divided the sea whose waves roared
In his article “Conjectural Emendation and the Text of the Book of Mormon”, in Brigham Young University Studies 18 (1978): 563–569, Stan Larson lists this example as a possible case where the current Book of Mormon text may be missing a part of the original text. Larson argues that the reference to the waves of the sea as the Lord’s waves doesn’t make sense. However, the Lord can control nature, so the waves of the sea can be considered his waves.
The original manuscript is extant here, and it clearly reads “God whose waves roared”. There is no sign of any insertion of the omitted phrase “that divided the sea”. In other words, this relative clause is missing from all the textual sources of the Book of Mormon.
It is perhaps worth noting that there are quite a few examples where some phrase or clause found in the Isaiah passages of the King James Bible is missing from the corresponding Book of Mormon text. Here are some of these omissions:
The Book of Mormon text also has numerous examples of additional phrases and clauses that are not found in the King James Bible. Given so many alterations of this nature, it is probably best not to emend any of these passages unless there is specific textual evidence for doing so. All of the omissions listed above may be intentional.
Summary: Unless there is information to the contrary, we accept cases of omitted phraseology in the biblical quotes in the Book of Mormon text; here in 2 Nephi 8:15, all the textual sources are missing the relative clause “that divided the sea” that occurs in Isaiah 51:15.