According to James Duke, in the middle of Alma's inspiring sermon concerning the priesthood to the apostate people of Ammonihah, Alma uttered a phrase that normally would be used to bring a sermon to a conclusion: "And thus it is, Amen" (Alma 13:9). However, Alma did not terminate his sermon but continued speaking. What, then, was the purpose of using such an expression in the middle of a sermon? In this case the phrase signals the completion of a chiasm, a literary form in which important ideas are presented and then repeated in reverse order. . . . In explaining the priesthood to the people of Ammonihah, Alma taught the doctrine of priesthood authority by expressing it in the form of a chiasm. He then called the attention of the people of Ammonihah to the chiastic structure of his sermon by uttering the phrase "And thus it is, Amen." (Alma 13:9). . . . The main chiasm is as follows:
A. order of his Son (13:2)
B. ordained (13:3)
C. called (13:3)
D. foreknowledge of God (13:3)
E. prepared (13:3)
F. foundation of the world (13:5)
G. Only Begotten Son (13:5)
H. high priesthood (13:6)
I. his rest (13:6)
H' high priesthood (13:7)
G' his Son (13:7)
F' foundation of the world (13:7)
E' prepared (13:7)
D' foreknowledge of all things (13:7)
C' called (13:8)
B' ordained (13:8)
A' order of the Son (13:9)
And thus it is, Amen.
In fact, Alma 13:1-9 not only contains a main chiasm, but four shorter chiasms and four alternates. [James T. Duke, "The Literary Structure and Doctrinal Significance of Alma 13:1-9 ," in Journal of Book of Mormon Studies, Spring 1996, F.A.R.M.S., pp. 103-105]