The language of this verse is clearly derived from the Ten Commandments:
Part of this language is repeated in the New Testament:
In the Hebrew for Exodus 20:11, the passage can be literally translated as “and all that in them”. In the King James translation, the verb is is in italics, which means that there is no be verb in the original Hebrew. The all can be interpreted as a singular with the meaning ‘everything’. Interestingly, the original Greek for Acts 4:24 agrees with the (Greek) Septuagint version of Exodus 20:11 and can be literally translated as “and all things in them”; there is no relative pronoun or be verb in the Greek, and the original word all has been made explicitly plural (equivalent to all things). But the King James translators chose to follow their own translation of Exodus 20:11 for Acts 4:24: “and all that in them is” (which is based on the original Hebrew of Exodus 20:11). Typically, New Testament authors quoted from the Greek version of the Hebrew Bible (the Septuagint), not the original Hebrew version. The King James translators apparently wanted to make sure that the New Testament citation followed the familiar language of the Ten Commandments, so they adopted William Tyndale’s original translation for Acts 4:24 (which dates back to 1526). Note, however, that the 1611 translators neglected to put the is in italics! Here the main point, as far as the Book of Mormon text is concerned, is that in both King James passages the be verb is in the singular (“and all that in them is”).
This particular phraseology from Exodus 20:11 and Acts 4:24 is frequently used in the Book of Mormon text. In addition to the example in 2 Nephi 2:14, we have these five examples (of which the Mosiah verse is a direct quote from Exodus 20:11):
We notice that in the Book of Mormon text, only one of the six passages has retained the original singular verb form is (namely, the one in Mosiah that explicitly cites Exodus 20:11). For the other five, the singular is has been edited to the plural are since each of these has the plural all things as the antecedent for the relative pronoun, either that or which. (Also note that the literal Mosiah quote is the only one that retains the reference to the sea.) In addition, the five paraphrastic examples replace the all with all things, as if each one were following the Greek (Septuagint) version of Exodus 20:11. Actually, this expansion in the Book of Mormon examples is just a natural extension of the original meaning rather than the result of some special access to the Septuagint. Otherwise, these five passages continue to follow the literalistic King James translation of Exodus 20:11: the phrase “that/which in them is” retains not only the relative clause construction but also the unnatural placement (for English) of in them before the verb is.
In any event, the five paraphrastic Book of Mormon examples show subject-verb disagreement between the antecedent all things and the main verb is (“all things that/which in them is”). The singular is in 2 Nephi 2:14 and in Alma 11:39 was changed to the plural are in the 1920 LDS edition. Joseph Smith changed the three others in his editing for the 1837 edition. (For a complete discussion of such editing, see subject-verb agreement in volume 3.) Of course, in all five cases the critical text will restore the original singular is since this is how the earliest textual sources read. Furthermore, such usage is in agreement with the biblical language of the King James Bible.
Summary: Maintain the singular verb form is in all six citations (or near citations) in the Book of Mormon of the language in Exodus 20:11 (“and all that in them is”); the earliest text consistently has the is, which agrees with the singular found in the King James Bible.