Here in the printer’s manuscript, scribe 2 initially wrote powers in the singular, but virtually immediately he corrected it to the plural (there is no change in the level of ink flow for the plural s that was inserted at the end of the line). This correction does not appear to be the result of conscious editing; instead, it seems to represent scribe 2’s attempt to copy th e text correctly. On the other hand, the 1830 edition reads in the singular, which could be interpreted as evidence that 𝓞 read in the singular and that scribe 2’s correction was an attempt at editing. This, however, seems unlikely since either reading will work here, at least in theory. In any event, whether a plural s was either added or lost here, it was probably accidental.
Elsewhere in the text, we have two instances of “the powers of heaven” but none of “the power of heaven”; both are found in this part of 3 Nephi:
The example from 3 Nephi 20:22 parallels 3 Nephi 21:25. Both, for instance, refer to “the power(s) of heaven” being in the midst of the people—and Jesus also will be in their midst. There is another similarity: as in 3 Nephi 21:25, scribe 2 of 𝓟 initially wrote Power in 3 Nephi 20:22 but then corrected it to Powers (in this case with slightly heavier ink flow). In 3 Nephi 20:22, however, the 1830 edition has the correct plural powers. This evidence argues that 3 Nephi 21:25 should also read in the plural as “the powers of heaven”. The critical text will therefore restore the plural powers here in 3 Nephi 21:25. Also note that the phrase occurs three times in the King James Bible, although in variant forms for a different expression:
David Calabro points out (personal communication) that one could interpret scribe 2’s correction of Power to Powers here in 3 Nephi 21:25 as the result of editing on his part, given that he had earlier corrected Power to Powers in 3 Nephi 20:22. One problem with this proposal is that in this case the two passages are not really that close: there are more than three manuscript pages separating the two instances. Moreover, scribe 2 of 𝓟 does not appear to ever engage in conscious editing of the text, unlike Oliver Cowdery and the 1830 typesetter. Although there is no other evidence of the 1830 typesetter mixing up the number for power(s), there is considerable evidence that he sometimes added or omitted the plural s, with about the same frequency as scribe 2 of 𝓟 (as explained under 3 Nephi 20:15).
Summary: Restore in 3 Nephi 21:25 the plural reading powers in “the powers of heaven”, the corrected reading in 𝓟; this reading agrees with the same plural use of powers for this phrase elsewhere in the text, especially in the parallel passage in 3 Nephi 20:22 (there scribe 2 of 𝓟 also initially wrote the correct powers in the singular).