We note here that the preposition by is not repeated before “the sword” in verse 22, but it is in verse 23. One wonders if perhaps the by was accidentally lost in verse 22, especially since in both verses the two preceding conjuncts have the preposition by (that is, “by famine and by pestilence”). And there are cases where the repeated preposition by was momentarily omitted by Oliver Cowdery as he copied from 𝓞 into 𝓟 (see the list under Alma 2:38). Perhaps here in Alma 10:22, Oliver omitted the by as he took down Joseph Smith’s dictation; or perhaps scribe 2 of 𝓟 omitted the by as he copied the text from 𝓞 into 𝓟.
One other example showing prepositional repetition when the nouns famine, pestilence, and sword are conjoined is found in the book of Helaman; in this case, the repeated preposition is with rather than by:
On the other hand, there is more general evidence that the preposition in a multiple conjunctive expression is sometimes not repeated in the original text, as in the following examples involving the preposition by:
One could argue that in each of these cases the repeated by is lacking when the two conjoined nouns are more closely associated with each other than with the other nouns in the conjunctive expression: smoke and vapor of darkness are nearly synonymous; Alma and Amulek were missionary companions before Zeezrom was converted; and Zenos was one of the prophets. On the other hand, one might suppose that famine, pestilence, and sword are equally distinct and that therefore there would not be any special association between pestilence and sword. Yet the text actually does associate them by referring to the pestilence of the sword—and in distinction to famine:
Thus we can find some justification for omitting the by in Alma 10:22, where pestilence and sword are conjoined. More generally, we do find conjunctive cases where the preposition just seems to be missing (that is, without any particular justification based on association). The evidence overall suggests that for cases involving repeated prepositions, it is best to follow the earliest textual sources and not try to maximize or minimize the repetition, even if this decision ends up allowing for considerable variety in the text (for a complete discussion, see under conjunctive repetition in volume 3).
So the question here in Alma 10:22–23 is whether we have an error or variation in the text. The safest solution is to follow the earliest textual sources and allow for the variation, although the possibility does remain that a by was omitted before the last conjunct in the conjunctive expression in verse 22.
Summary: Accept in Alma 10:22–23 the variation between “by famine and by pestilence and the sword” (verse 22) and “by famine and by pestilence and by the sword” (verse 23); the language in Helaman 11:14 suggests that the repeated by is not necessary between pestilence and the sword.