The use of of after promise appears to be unnecessary, almost as if it occurs in anticipation of the many following of ’s (“of the Lord of the fruit of my loins”). The 1852 LDS edition dropped this seemingly extra of, but the RLDS text has retained it.
In a phrase like “promise of X”, the preposition of can either mean ‘from’ or ‘regarding’, as in the following two examples from this same chapter:
From these examples we may deduce that 2 Nephi 3:14 should be interpreted as meaning ‘for this promise / which I have obtained from the Lord regarding the fruit of my loins / shall be fulfilled’.
The problem with the extra of that heads the relative clause (“this promise of which I have obtained”) is that it seems disconnected from the rest of the relative clause. In similar passages in the text (six of them), the relative pronoun which acts alone as the complement of the verb obtain, as in this nearby example:
A reading with an extra of (“the land of promise of which they had obtained”) would seem anomalous; we expect only “X obtains Y”, not “X obtains of Y”.
There are two possibilities regarding the additional of that heads the relative clause in 2 Nephi 3:14: the extra of was accidentally added during the early transmission of the text; or the extra of is actually intended, even though it seems superfluous or distracting to English readers.
The first possibility (of accidentally adding the of ) could have occurred at various stages in the transmission: Joseph Smith could have added the of when he read off the text, or Oliver Cowdery could have added it either when he took down Joseph’s dictation or when he copied from 𝓞 into 𝓟 (the original manuscript is not extant here). There is minor evidence elsewhere in the manuscripts for this kind of error. Consider the following two instances where Oliver, as he copied from 𝓞 into 𝓟, initially added an unnecessary of at the head of a relative clause. In both cases, Oliver corrected his error in 𝓟:
On the other hand, there is also evidence for the second possibility (namely, the of is intended). There are a couple of examples in the earliest text that have an extra of that seems intended, even though it appears to be unnecessary:
In the first instance, Joseph Smith removed the extra of in his editing for the 1837 edition. In the second instance, the 1920 LDS edition omitted not only the extra of but also the definite article the. The RLDS text has retained the original of the which, showing that the use of the extra of in Alma 58:3 is not egregious. Nor does the earliest text for Alma 51:14 sound particularly objectionable. We can probably make the same claim for the earliest text in 2 Nephi 3:14 since there the RLDS text has also retained the extra of. Of course, all three of these cases could be examples of the of being accidentally added during the early transmission of the text. But given the tendency for the text to maintain these extra of ’s, the critical text will follow the evidence of the earliest textual sources, thus restoring the of in 2 Nephi 3:14, Alma 51:14, and Alma 58:3.
Summary: Restore the original of at the head of the relative clause in 2 Nephi 3:14 (“this promise of which I have obtained of the Lord”); similar examples of this usage in the earliest text are found in Alma 51:14 and Alma 58:3, although it is possible that all three of these examples are due to scribal error.