As Nephi has done previously, he uses scriptural events to inform his current events. In this case, he returns to Moses leading the children of Israel from Egypt, which also gives him the connection to Joseph, who is Nephi’s lineage ancestor.
The message is about the atoning Messiah, so the event selected is salvation from death. Moses saved those who would have died from the serpent bite by having them look to a symbol. The implication is that the Messiah becomes the embodiment of that symbol. Moses providing water to a nation, that, otherwise, would die of thirst again, saves them. Symbolically, the Messiah is that water, a connection John made explicit in John 4:10 and 11.