Why would Joseph Smith have thought to repeatedly mention “stretching forth one’s hand” before an important speech?

Multiple scriptures in the Book of Mormon reference stretching forth one’s hand before an important speech. David Calabro lists 10 instances as follows:

And the Lord said unto me: Stretch forth thy hand and prophesy, saying . . . (Mosiah 12:2)
After Abinadi had spoken these words he stretched forth his hands and said . . . (Mosiah 16:1, printer’s manuscript)
But Amulek stretched forth his hand, and cried the mightier unto them, saying . . . (Alma 10:25)
When Alma had said these words unto them, he stretched forth his hand unto them and cried with a mighty voice, saying . . . (Alma 13:21)
And when he saw them he stretched forth his hand, and besought them that they would heal him. (Alma 15:5)
And as he arose, he stretched forth his hand unto the woman, and said . . . (Alma 19:12)
Therefore he did say no more to the other multitude; but he stretched forth his hand, and cried unto those which he beheld, which were truly penitent, and saith unto them . . . (Alma 32:7)
Therefore he went and got upon the wall thereof, and stretched forth his hand and cried with a loud voice, and prophesied unto the people whatsoever things the Lord put into his heart. (Helaman 13:4)
And it came to pass that he stretched forth his hand and spake unto the people, saying . . . (3 Nephi 11:9)
He stretched forth his hand unto the multitude, and cried unto them, saying . . . (3 Nephi 12:1)

This seems a rather deliberate yet unexpected inclusion by Joseph Smith in the Book of Mormon, but the gesture of stretching forth one’s hand before an important speech has deep Mesoamerican and Egyptian roots.

How would Joseph know about this small detail and use it so consistently?

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