Why is there gradation in the Book of Mormon just like the Old and New Testaments?

Gradation is a form of parallelism found in the Old and New Testament (as well as the Book of Mormon) which occurs when the same word or words are found in successive clauses or sentences.

An example from the Bible is the following on Joel 1:3-4

Tell ye
your children of it, and let
your children tell
their children, and
their children another generation. That which the palmerworm hath left hath the
locust eaten; and that which the
locust hath left hath the
cankerworm eaten; and that which the
cankerworm hath left hath the
caterpiller eaten.

One example from the Book of Mormon is found in Alma 42:17-20

Now, how could a man repent except he should
sin? How could he
sin if there was no
law? How could there be a
law save there was a
punishment? Now, there was a
punishment affixed, and a just
law given, which brought remorse of conscience unto man. Now, if there was no
law given—if a man murdered he should
die—would he be afraid he would
die if he should murder? And also, if there was no law given against
sin men would not be afraid to
sin.

How did Joseph Smith know about gradation? If it appears in the Book of Mormon by chance then why does gradation appear mainly in sermons, letters and prophecies?

See:

Evidence Central – Book of Mormon Evidence: Gradation

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