For the third printing of the 1905 LDS Chicago edition (in 1907), the pronoun he was added to the last clause of this passage. All subsequent LDS editions, from 1911 on, have followed this reading with the he. The selection of he is consistent with the verb form has, which is found in all the (extant) textual sources. The editing here suggests the possibility that he might have been accidentally lost during the early transmission of the text.
In the original Book of Mormon text has is normally restricted to third person singular subjects. Yet there are a few cases in the original text where has clearly took a plural subject; as might be expected, all of these plural uses of has have been edited to have:
In fact, the original use of the singular has in Mosiah 7:20 is not particularly difficult since there already is a preceding singular it is in the sentence (“and behold it is because of our iniquities and abominations that has brought us into bondage”).
What really causes difficulty in this passage is the phrase because of; speakers of modern English expect the passage to read “and behold it is our iniquities and abominations that has brought us into bondage”—that is, we would prefer for this sentence to read without the phrase because of. Yet the current Book of Mormon text actually has a second example of this usage:
The expected phraseology in English would be “for it is the traditions of their fathers that causeth them to remain in their state of ignorance”. The existence of this second example with because of argues that the earliest reading in Mosiah 7:20 is indeed intended and should therefore be accepted as the correct reading.
The addition of he into the LDS text has also created an exception in the text. In all other passages discussing people being brought into bondage, where the verb is bring, the agent (if identified) is always a human agent, not God. In other words, God himself does not “bring people into bondage”; rather, others do, or people may “bring themselves into bondage” by their own actions:
Mosiah 7:22 and all this he done for the sole purpose of bringing this people into subjection or into bondage
Mosiah 9:10 now it was the cunning and the craftiness of king Laman to bring my people into bondage
Mosiah 9:11 they could not overpower them and bring them into bondage Mosiah 9:12 therefore they were desirous to bring us into bondage
Mosiah 11:21 yea and they shall be brought into bondage Mosiah 11:23 they shall be brought into bondage
Mosiah 12:2 this generation because of their iniquities shall be brought into bondage
Mosiah 23:23 they were brought into bondage
Mosiah 29:18 and also because of their iniquities they were brought into bondage
Alma 5:5 they were brought into bondage by the hands of the Lamanites Alma 43:8 and also that he might gain power over the Nephites by bringing them into bondage
Alma 43:29 it was their intention ... to subject them and bring them into bondage
Alma 44:2 neither do we desire to bring any one to the yoke of bondage Alma 44:7 yea we will see who shall be brought into bondage
Alma 48:4 for he was determined ... to overpower the Nephites and to bring them into bondage
The Lord or his prophets, on the other hand, can “bring people out of bondage”:
1 Nephi 17:25 wherefore ye know that it must needs be a good thing for them that they should be brought out of bondage
Mosiah 12:34 I am the Lord thy God which have brought thee out of the land of Egypt / out of the house of bondage Alma 9:22 having been delivered of God ... by the hand of the Lord …
having been brought out of bondage time after time
These same restrictions on the use of the specific phrase “bring into bondage” hold in the King James Bible: the Lord never “brings people into bondage”, but he can, of course, “bring them out of bondage” (note, for instance, that Mosiah 12:34, cited above, is quoting Exodus 20:2). Thus the emended LDS text in Mosiah 7:20 is inconsistent with all other usage in the Book of Mormon and the biblical text. This systematicity in the text supports restoring the original reading in Mosiah 7:20 (“and behold it is because of our iniquities and abominations that has brought us into bondage”); in other words, the people were brought into bondage because of their own evil deeds.
Summary: Restore the earliest reading in Mosiah 7:20: “it is because of our iniquities and abominations that has brought us into bondage”; this construction is supported by the reading in Alma 9:16; the addition of he in the LDS text creates an exceptional reading: elsewhere the Book of Mormon text never specifically states that the Lord himself “brings people into bondage”.