The second part of this verse, based on the earliest textual sources, seems to be missing its verb phrase. Elsewhere in the text, we do not find long yea- clauses like this for which the whole verb phrase has been ellipted.
For the third printing (in 1907) of the 1905 LDS missionary edition, the verb phrase “shall rise” was inserted, presumably by German Ellsworth (the mission president in charge of publishing that missionary edition of the Book of Mormon). This reading has been followed in all subsequent LDS editions.
The first part of this verse parallels the second part and suggests that the missing verb phrase is “shall be lifted up”. Note that both refer in the beginning to “in a day when …” and end with the same phrase “in the pride of their hearts”. In fact, when we look elsewhere in the text, we find numerous examples that refer to people “lifted up in pride”:
In fact, six of these have precisely the same phraseology: “in the pride of their hearts”. There is also one other passage that refers to churches being lifted up, just like here in Mormon 8:28:
The surrounding passage also refers to pride. (For discussion on how to parse the larger passage, see under 2 Nephi 28:11–12.)
Another possible emendation here in Mormon 8:28 would be to supply “shall be puffed up”, thus “when leaders of churches and teachers shall be puffed up in the pride of their hearts”. There are a few cases where the text refers to people being “puffed up in pride”:
And there are a few other examples of “in one’s pride”, each with a different verb:
But nowhere do we find cases of people “rising (or raising) up in pride”. It seems very reasonable here in Mormon 8:28 that some verb phrase is missing and that the best emendation would be “shall be lifted up”, especially given that phraseology earlier in the verse (“and shall be lifted up in the pride of their hearts”).
Of course, here in Mormon 8:28, by adding the verb phrase “shall be lifted up” to the text, we assume that this rather long verb phrase was accidentally lost when Joseph Smith dictated the text to Oliver Cowdery, here the presumed scribe in 𝓞. (Since both 𝓟 and the 1830 edition agree in their reading here and are firsthand copies of 𝓞, the lack of a verb phrase in those two sources means that probably 𝓞 too was missing it.) Although long phrases were sometimes temporarily skipped when the text was initially written down in 𝓞, the text was soon corrected. There isn’t much evidence in 𝓞 for the permanent loss of longer phrases, but that may be because the resulting shorter text in most cases would have been perfectly acceptable. In any event, such permanent losses were probably infrequent. But here in Mormon 8:28 we seem to have one that is noticeable, although one could argue that Mormon himself accidentally omitted the verb phrase here. If we could be sure that this was the case, we would not emend the critical text reading (despite its difficulty).
Summary: Emend Mormon 8:28 to read “when leaders of churches and teachers shall be lifted up in the pride of their hearts”; this verb phrase is supported by numerous other occurrences of this phraseology in the text, including the first part of Mormon 8:28 itself.