Here in the 1840 edition the plural parts was changed to the singular part, perhaps by Joseph Smith in his editing for that edition. The singular reading has been maintained in the RLDS textual tradition. The 1920 LDS edition introduced the singular part into the LDS text, perhaps by reference to the 1840 edition or simply because the 1920 editors found that “the more parts of the Nephites” sounded odd. The original manuscript is not extant here. If the original text read in the singular as part, the change to parts could have been prompted by the preceding rhyming plural, hearts, thus replacing “the hearts of the more part of the Nephites” with “the hearts of the more parts of the Nephites”. Such a change could have happened during the dictation of the text or when Oliver Cowdery copied the text from 𝓞 into 𝓟.
The singular form, more part, is considerably more frequent in the Book of Mormon text than the plural, more parts. There are 24 instances of the singular; in all cases but one the determiner is the (the one exception, marked below with an asterisk, takes a as the determiner):
In addition, there are 14 instances where there is an adjective occurring between more and part; once more, the determiner is the except for one case of a (marked below with an asterisk):
In contrast to these 14 instances of the singular “more part”, the text has a number of instances of the plural “more parts”, including one verse where the phrase is repeated in a corrective or-clause (Alma 43:38):
For the nouns wilderness, body, and land, there is independent evidence in the text that these nouns actually have parts:
Although there is no independent evidence in the text for “parts of prophecies” (as implied by 1 Nephi 19:3), the statement that Nephi should write down “the more plain and precious parts” of their prophecies seems fully appropriate.
There is one instance of more parts elsewhere in the text, and this one occurs without an intervening adjective, just like the earliest extant reading for Helaman 6:21:
Interestingly, the printer’s manuscript for this passage reads in the singular (“the more part of his gospel”). For that part of the text, both the 1830 edition and 𝓟 are firsthand copies of the original manuscript, so either the 1830 edition or 𝓟 may represent the reading in 𝓞, no longer extant in 4 Nephi. If 𝓞 read in the singular, then the 1830 typesetter added the plural s. If 𝓞 read in the plural, then scribe 2 of 𝓟 omitted the plural s. Since the plural parts is the unexpected reading for modern English speakers, the most likely scenario in 4 Nephi 1:27 is that 𝓞 read in the plural and scribe 2 of 𝓟 dropped the unexpected plural s. We can find evidence for one case where the scribe replaced the plural parts with the singular part (in that case, the scribe was Oliver Cowdery). For discussion of that possibility, see under Jacob 5:13–14.
As with all but one of the six plural cases of “more parts”, we can find specific evidence for “parts of the gospel” elsewhere in the text:
Since the Book of Mormon text does refer to different parts of the gospel, the use of “the more parts of his gospel” in 4 Nephi 1:27 is acceptable and will be maintained in the critical text.
Most of the examples of “more part” and “more part” involve people (28 out of the 38 instances, including all 9 instances where part is postmodified by of them). Given this regularity, one could argue that the one case of “the more parts of the Nephites”, here in Helaman 6:21, is most likely an error for “the more part of the Nephites”. The ultimate question, however, is whether one can refer to parts of a people. When we look at the entire text, we find that the text virtually always refers to “part of a people” rather than to “parts of a people”. But there is one clear exception:
Here there is no question that the original text reads parts since its determiner is the plural those. In other words, this example definitely shows that “the more parts of the Nephites” in Helaman 6:21 is possible. The critical text will therefore restore the plural parts in Helaman 6:21, the earliest extant reading, even though it could be an error for part.
Summary: Accept the two original instances in the text of more parts, here in Helaman 6:21 (“the more parts of the Nephites”) and in 4 Nephi 1:27 (“the more parts of his gospel”); this usage is supported by six instances in the text of “more parts of X”; in addition, there is clear evidence that the text can refer to “parts of a people” as well as to “parts of the gospel”.