In the 1920 LDS edition, the conjunction for in front of “I desire” was deleted in order to create an independent clause for this passage. One could view the for here as the result of an early error in the text, perhaps the result of there being two other instances of the conjunction for in this passage. The 1920 edition made the same emendation later in the text:
In this instance, the 1920 edition also deleted a repeated being, but ultimately the purpose for deleting the conjunction for was to create an independent clause for the passage. Note in this second example that there is no other for in the passage that could have prompted the for that does occur. In fact, both Mosiah 29:5 and Ether 1:34 are similar in that the for comes between a preceding subordinate clause and the following main clause. In Mosiah 29:5, we have the parenthetical clause “for I esteem you as such”, which modifies the noun phrase “my brethren”; in Ether 1:34, we have the conjunctive present participial clause “being a large and a mighty man and being a man highly favored of the Lord”, which modifies the preceding noun phrase “the brother of Jared”. These two examples suggest that the for is being intentionally used to separate the preceding parenthetical clause from the following main clause. For this reason, the critical text will restore the for in both Mosiah 29:5 and Ether 1:34.
It should also be pointed out that the conjunction for is frequently repeated in the Book of Mormon, including the following case where we get six occurrences in a row:
The multiple use of the conjunction for often seems to be acting more as a simple separator between clauses rather than as a chain of explanation between the clauses.
David Calabro (personal communication) provides another type of example where for is used more as a simple separator—namely, in the narrative-initial clausal construction “for it came to pass”:
Summary: Restore in Mosiah 29:5 the use of the conjunction for between the preceding parenthetical clause “for I esteem you as such” and the following main clause “I desire that ye should consider the cause”; Ether 1:34 provides a similar example of this use of the conjunction for as a clausal separator.