Ross Geddes suggests (personal communication, 28 November 2004) that this sentence may be missing my (and also possibly beloved ) before brethren. In this sermon of Mormon’s, we otherwise have only “my brethren” (four times) and “my beloved brethren” (nine times). However, with the verb beseech, the use of brethren alone may be correct given that in Paul’s epistles (in the King James Bible) there are ten instances of the verb beseech occurring with just brethren, as in this sampling:
There is also one example in Hebrews 13:22: “and I beseech you brethren”. The Book of Mormon has only one other relevant case with the verb beseech: “wherefore my beloved brethren / I beseech of you” (Jacob 6:5). Here, of course, the placement of the vocative is initial rather than at the end, and it is the full form, “my beloved brethren”, rather than just the word brethren.
There is one case in the printer’s manuscript where Oliver Cowdery initially omitted beloved from the phrase “my beloved brethren”:
𝓞 is mostly extant here, reading beloved Brethren at the beginning of a manuscript line. But there is no specific evidence for an original my being omitted from “my brethren” or, even less probably, my beloved from “my beloved brethren”. (There is one case where the 1830 typesetter added beloved to “my brethren”, in Alma 34:28.)
The most convincing argument against the suggested emendation here in Moroni 7:19 is that brethren alone is twice used as a vocative in the book of Jacob:
Thus there is no strong reason to reject the use of brethren alone in Moroni 7:19. The critical text will retain the earliest reading in Moroni 7:19: “wherefore I beseech of you brethren”.
Summary: Maintain in Moroni 7:19 the use of brethren alone as a vocative since there are two other instances of such usage in the text (in Jacob 4:8, 10); in addition, King James usage in the New Testament epistles supports the use of brethren alone as a vocative when the verb is beseech.