The original manuscript reads “the souls of man”, a mixture of plural and singular. This is possible if we interpret man as semantically plural, meaning ‘mankind’. Even so, Oliver Cowdery emended the singular to the plural men when he copied the text from 𝓞 to 𝓟, thus ending up with both nouns in the plural (“the souls of men”).
Elsewhere in the Book of Mormon, there are seven occurrences of “the souls of men”, so this emendation seems quite possible:
There is also one case where both nouns are in the singular:
But there are no other occurrences of mixed number (like “the souls of man” or “the soul of men”).
Further, there are quite a few cases in the manuscripts where the scribe initially wrote either man or men and then changed it to read the opposite, perhaps in the same manuscript or in copying from 𝓞 into 𝓟:
Confusion between man and men is therefore fairly frequent.
But there is another possibility: perhaps scribe 2 of 𝓞’s souls is an error for soul. We have manuscript evidence that on two different occasions scribe 2 accidentally added a plural s:
Thus it is quite possible in 1 Nephi 15:35 that scribe 2 of 𝓞 accidentally wrote the plural souls instead of the correct singular, soul.
But the crucial factor in interpreting 1 Nephi 15:35 is an earlier verse where the brothers ask about “the final state of the soul”:
Thus in verse 35, Nephi answers his brothers’ question, and the text there should correctly read “the final state of the soul of man”, parallel to verse 31. We can therefore assume that in verse 35, scribe 2 of 𝓞 accidentally added a plural s to soul when he took down Joseph Smith’s dictation. The corresponding occurrence of the singular man in 𝓞 therefore represents the original reading and should not have been emended to men.
Summary: Emend 1 Nephi 15:35 to read “the final state of the soul of man”, which differs from 𝓞 in having the singular soul in place of the plural souls; 1 Nephi 15:35 answers the earlier question in 1 Nephi 15:31 that refers to “the final state of the soul”.