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Chiasmus

  <<John W. Welch, as a young missionary in Germany in 1967, discovered Chiasmus in the Book of Mormon.
Then later in 1969, "...John announced in an academic journal the remarkable discovery that an ancient and highly specialized Hebrew literary style could be found throughout the Book of Mormon. A world-famous, non-Mormon scholar called it the “most stunning information I’ve learned concerning the Book of Mormon.”
 
Chiasmus are writings, phrases of words, grammatical constructions, or concepts that are stated and then in some way repeated in a reverse order. 

Chiasmus in the Book of Mormon are evidence of an ancient Hebrew origin. It is just one of several complex forms of literary parallelism that are common to other ancient Semitic writings. 

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Bible Chiasmus:

The ancient Hebrew and Greek texts of the Old and New Testaments are full of Chiasmus.  Many of these have become lost in translation, but hundreds of others remain.

Example; (Matthew 19:30)

      “But many that are first
       B.     shall be last:
       B.     and the last
  A.     shall be first       

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Book of Mormon Chiasmus:

Chiasmus was not searched for or discovered in the Book of Mormon until the late 1960s. 

 Example;  (Alma 39:9)

  A.    “For it is expedient that an atonement should be made;
     B.     for according to the great plan of the Eternal God there must be an atonement made,
       C.     or else all mankind must unavoidably perish;
         D.      yea, all are hardened;
         D.      yea, all are fallen and are lost,
       C.      and must perish
    B.     except it be through the atonement
  A.    which it is expedient should be made.”

The entire chapter of Alma 36 is a Chiasmus.
See: Come Follow Me (Insights into Alma 36-38, Book of Mormon Central)

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Additional Information:

Book of Mormon Central Videos:
...  How Much Could Joseph Smith Have Known about Chiasmus in 1829? #334

...  What Counts as Chiasmus?  #337

...  How Did Biblical and Ancient Near Eastern Authors Use Chiasmus?  #340

...   Can Chiasmus Survive Translation?  #343

...  Was Chiasmus Known to Ancient American Writers?  #346

...  How was Chiasmus Discovered in the Book of Mormon?  #353

...  Does Chiasmus Prove Anything about the Book of Mormon?  #358
 

The Amazing True Story of How Chiasmus was Discovered in the Book of Mormon.  (10:05 min.)(Greg. Welch.)

Chiasmus in the Book of Mormon  (John W. Welch, Ensign Feb. 1972)

Chiasmus in the Book of Mormon (FAQ: Mormon Answers)

Chiasmus in Mayan Text. (Allen J. Christenson, Ensign Oct. 1988)