1 Nephi 17:41
41 And he did straiten them in the wilderness with his rod; for they hardened their hearts, even as ye have; and the Lord straitened them because of their iniquity. He sent fiery flying serpents among them; and after they were bitten he prepared a way that they might be healed; and the labor which they had to perform was to look; and because of the simpleness of the way, or the easiness of it, there were many who perished.
The event Nephi was describing is mentioned in the Old Testament,{1} but its meaning is not discussed there (Numbers 21:4-9). To learn its meaning we have to go to the Book of Mormon where we find that the serpent symbolized the Savior as the Messiah. It was a later Nephi who explained that it represented the Atonement of “the coming of the Messiah” (Helaman 8:13-16).
The Savior referred to that Old Testament event when he spoke with Nicodemus. If we read the story of Nicodemus as being the Savior’s teaching that great, good, and learned man about who he (Jesus/Jehovah/Messiah) really was, then we see his statement about Moses’s brass serpent as an explanation that Jesus is the Messiah of whom Moses testified (John 3:14-21).
—————————————
FOOTNOTE
{1} The brass serpent, but not the incident, is mentioned again but with a negative connotation. It was worshiped as a false god, and king Hezekiah had it destroyed (2 Kings 18:4)
<><><><><><><><><><><><><><><><><><><><><><><><>