According to Donald Parry, the prevalent poetic form of the canon of scripture is not the ode, the lamentation, nor the psalm, but parallelism. Chiasmus is a form of inverted parallelism in which the flow of ideas move progressively to the most important central point, and then flow outward in the exact same parallel fashion. This parallel inward/outward flow of ideas is symbolized by the Greek letter chi representing the letter "x".
Helaman 6:21-26 talks of Satan, the Gadianton band, and their oaths and covenants of wickedness. According to Parry, the key elements of these verses have been recorded in chiastic form in order to emphasize the message of the author, and appear as follows:
A. But behold, Satan
B. did stir up the hearts of the more part of the Nephites,
C. insomuch that they did unite with those bands of robbers,
D. and did enter into their covenants and their oaths,
E. that they would protect and preserve one another in whatsoever difficult circumstances they
should be placed.
F. that they should not suffer for their murders, and their plunderings, and their stealings.
G. And it came to pass that they did have their signs, yea, their secret signs, and their
secret words;
H. and this that they might distinguish a brother who had entered into the covenant,
I. that whatsoever wickedness his brother should do
H' he should not be injured by his brother,
G' nor by those who did belong to his band, who had taken this covenant.
F' And thus they might murder, and plunder, and steal, and commit whoredoms and
all manner of wickedness, contrary to the laws of their country and also the laws of their God.
E' And whosoever of those who belonged to their band should reveal unto the world of their
wickedness and their abominations, should be tried, not according to the laws of their
country, but according to the laws of their wickedness, which had been given by Gadianton
and Kishkumen.
D' Now behold, it is these secret oaths and covenants which Alma commanded his son should not go
forth unto the world, lest they should be a means of bringing down the people unto
destruction. Now behold, those secret oaths and covenants did not come forth
C' unto Gadianton from the records which were delivered unto Helaman;
B' but behold, they were put into the heart of Gadianton
A' by that same being who did entice our first parents to partake of the forbidden fruit--
[Donald W. Parry, The Book of Mormon Text Reformatted according to Parallelistic Patterns, p. 353]