Here scribe 2 of 𝓟 initially wrote “save it is the transgressions of my people”—that is, he wrote the plural transgressions. But he immediately corrected the text to the singular transgression by erasing the word-final plural s. In general, the earliest text allows either singular or plural forms for the noun transgression, with 31 of the singular and 13 of the plural. Scribe 2 of 𝓟 tended to accidentally write the plural in place of the singular, as noted in two out of the three other cases where he was required to copy the singular transgression:
Elsewhere in the text, we consistently get the singular “transgression of X” when X refers to Adam and Eve eating the forbidden fruit in the garden (which was a single transgression):
More generally, we normally get the plural transgressions in the phrase “transgression(s) of X”, where X is semantically plural:
When we expand our search to include “their transgression(s)”, we find that the original text is evenly divided between the singular and plural:
The tendency in the transmission of the text has been to replace the singular with the plural, not only here in Mosiah 27:13 but also in Alma 3:6 and Alma 9:23 by scribe 2 of 𝓟 (see above) as well as once by Oliver Cowdery as he copied from 𝓞 into 𝓟:
These more general results suggest that we should follow the earliest textual sources in determining whether transgression should be singular or plural when postmodified by a prepositional phrase headed by of.
Summary: Maintain in Mosiah 27:13 the singular form transgression, the immediately corrected reading in 𝓟 (“and nothing shall overthrow it save it is the transgression of my people”).