Why would Joseph Smith use beginning and ending repetitions while dictating the Book of Mormon?

One form of parallelism is that of repetitive beginnings or repetitive endings. 3 Nephi 9:3-11 contains an example of this in which a lengthy phrase is repeated at the end of each passage.

Behold, that great city Zarahemla have I burned with fire, and the inhabitants thereof.
And behold, that great city Moroni have I caused to be sunk in the depths of the sea, and the inhabitants thereof to be drowned.
And behold, that great city Moronihah have I covered with earth, and the inhabitants thereof, to hide their iniquities and their abominations from before my face, that the blood of the prophets and the saints shall not come any more unto me against them.
And behold, the city of Gilgal have I caused to be sunk, and the inhabitants thereof to be buried up in the depths of the earth;
Yea, and the city of Onihah and the inhabitants thereof, and the city of Mocum and the inhabitants thereof, and the city of Jerusalem and the inhabitants thereof; and waters have I caused to come up in the stead thereof, to hide their wickedness and abominations from before my face, that the blood of the prophets and the saints shall not come up any more unto me against them.
And behold, the city of Gadiandi, and the city of Gadiomnah, and the city of Jacob, and the city of Gimgimno, all these have I caused to be sunk, and made hills and valleys in the places thereof; and the inhabitants thereof have I buried up in the depths of the earth, to hide their wickedness and abominations from before my face, that the blood of the prophets and the saints should not come up any more unto me against them.
And behold, that great city Jacobugath, which was inhabited by the people of king Jacob, have I caused to be burned with fire because of their sins and their wickedness, which was above all the wickedness of the whole earth, because of their secret murders and combinations; for it was they that did destroy the peace of my people and the government of the land; therefore I did cause them to be burned, to destroy them from before my face, that the blood of the prophets and the saints should not come up unto me any more against them.
And behold, the city of Laman, and the city of Josh, and the city of Gad, and the city of Kishkumen, have I caused to be burned with fire, and the inhabitants thereof, because of their wickedness in casting out the prophets, and stoning those whom I did send to declare unto them concerning their wickedness and their abominations.
And because they did cast them all out, that there were none righteous among them, I did send down fire and destroy them, that their wickedness and abominations might be hid from before my face, that the blood of the prophets and the saints whom I sent among them might not cry unto me from the ground against them. (emphasis added)

How would Joseph Smith have been able to dictate this form of parallelism? How could he remember the same phrase and end each passage the same way?

See:

Evidence Central – Book of Mormon Evidence: Beginning and Ending Repetitions

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