This variant has significant ramifications for the meaning. The reading of the original manuscript seems to limit the “raising up of seed” to the women. Oliver Cowdery added the subject pronoun they when he copied the text into 𝓟. This emendation also changed the grammatical category for the that, from a relative pronoun (with daughters as the antecedent) to a subordinate conjunction (with the meaning ‘in order that’, thus making the that-clause adverbial).
Elsewhere in the text, we find a number of passages that refer to the Lord raising up offspring (referred to as seed or a branch):
Several examples in the King James Bible also refer to the Lord’s ability to raise up offspring:
But the emended text in 1 Nephi 7:1 refers to they, not the Lord, as raising up seed. Such usage is not found elsewhere in the Book of Mormon text, but it is found in the King James Bible in reference to a male being required to marry his brother’s widow and father children in place of the dead brother:
In each of these biblical passages, the crucial aspect centers on the male’s role in physically producing offspring. Such a focus implies that in 1 Nephi 7:1, the antecedent for the subject pronoun they is actually “his sons”. Thus if Oliver Cowdery’s they is accepted, it should probably be interpreted as referring to the sons of Lehi rather than their wives or even all of them together as parents.
From a scribal point of view, we know that scribe 3 of 𝓞 tended to drop the subject pronoun I (see the discussion under 1 Nephi 5:8). If Oliver Cowdery’s emendation here in 1 Nephi 7:1 is correct, then we would also have an example of scribe 3 dropping they. Nonetheless, we have no specific evidence elsewhere that this scribe tended to drop the subject pronoun they.
Since scribe 3 of 𝓞 sometimes dropped the I, we should briefly consider the possibility that I might have been the missing subject in 1 Nephi 7:1:
that it was not meet for him Lehi
that he should take his family into the wilderness alone
but that his sons should take daughters to wife
that I might raise up seed unto the Lord
We have already seen that this passage is an indirect quote (see the previous discussion regarding saying for this verse), so obviously any reading with I is impossible, no matter whether I refers to Lehi or Nephi. Nor will the pronouns we and ye work here because of the indirect quote. The pronoun he might work here if we take Lehi as the antecedent. But the emphasis is on getting wives for his sons; thus they does seem to be the most plausible subject pronoun, especially in light of the corresponding biblical passages referring to males raising up seed.
There is considerable internal evidence that some subject is missing in 𝓞. Elsewhere in the Book of Mormon text, there are no examples of the relative pronoun that directly followed by the modal verb might, but there are numerous examples of the subordinate conjunction that followed by a pronoun and then might:
that I might 44 times that thou mightest 6 times that he might 76 times that she might 1 time that it might 5 times that we might 25 times that ye might 26 times that they might 184 times that there might 1 time
There are also 54 examples of nonpronominal subject noun phrases preceded by the subordinate conjunction that and followed by the modal verb might. Even if we consider the relative pronouns which and who (alternatives to the relative pronoun that), there are no occurrences directly followed by might. When compared with which and who, the relative pronoun that is fairly rare in the Book of Mormon, so the use in 𝓞 of that as a relative pronoun is highly unexpected. The subordinate conjunction that, on the other hand, is very common, especially in cases involving the conditional modal might (as shown by the statistics just listed).
Summary: Based on evidence from biblical usage, Oliver Cowdery’s emended they in 1 Nephi 7:1 should be accepted; usage elsewhere in the Book of Mormon strongly suggests that the reading in 𝓞 (“that might raise up seed”) is highly improbable.