As explained in the history of the 1830 edition (see volume 3 of the critical text), somewhere between verses 7 and 18 of Helaman 13 (inclusively), the 1830 compositor started to set type from the original manuscript rather than its copy, the printer’s manuscript. He continued setting type from 𝓞 until he got to the end of Mormon. Since we cannot be precisely sure where in Helaman 13 the switch to 𝓞 took place, we must consider whether here in verse 16 the 1830 edition was set from 𝓞 or from 𝓟. If from 𝓟, then we can be sure that the 1830 compositor is responsible for the loss of the repeated the in “the wickedness and the abominations”. If the 1830 compositor set his type from 𝓞, then he may have still been the one responsible for omitting an original repeated the. But in that case it is also possible that 𝓞 itself did not have the repeated the and that the 1830 compositor correctly set the text without the repeated the; under this alternative, Oliver Cowdery, the scribe in 𝓟, accidentally added the repeated the as he copied from 𝓞 into 𝓟.
Nearby we have three other examples of wickedness conjoined with abominations, namely, two preceding instances (in verses 14 and 15) and one following (in verse 17):
The two preceding instances lack the repeated the (both read “the wickedness and abominations which is in her”). On the other hand, the following instance (in verse 17) repeats the determiner, in this case their: “their wickedness and their abominations”. It seems quite reasonable that the 1830 compositor could have been influenced by the two instances of “the wickedness and abominations” in verses 14 and 15 to omit in verse 16 the repeated the in the phrase “the wickedness and the abominations”. It seems less likely that Oliver Cowdery would have added a repeated the in 𝓟, especially given the two preceding instances without the repetition.
More generally, there are eight other occurrences of “the wickedness and abominations” in the text, but only one of “the wickedness and the abominations”. Interestingly, this single exception was initially written in 𝓟 as “the wickedness and abominations”, but then almost immediately Oliver Cowdery corrected the text by supralinearly inserting the repeated the:
There would have been no motivation to add the repeated the in this other case unless it was actually in 𝓞. Thus “the wickedness and the abominations” was most probably the reading of the original text in Mosiah 3:7. We also note here that there are many more examples in the history of the text where the repeated the has been accidentally omitted rather than added (see the list under conjunctive repetition in volume 3). In English, the repeated the is not expected; thus it is more likely that the 1830 compositor is the one responsible for the textual variant here in Helaman 13:16. The critical text will therefore restore the more difficult reading in Helaman 13:16, “because of the wickedness and the abominations which is in them”.
Summary: Restore in Helaman 13:16 the repeated the, the reading in 𝓟 (“the wickedness and the abominations which is in them”); the two preceding cases of this expression, in verses 14 and 15, lack the repeated the (“the wickedness and abominations which is in her”), which apparently led the 1830 compositor (irrespective of whether he set the text from 𝓞 or 𝓟) to accidentally omit the repeated the.