According to Andrew Skinner, the serpent first appears in the scriptures in the story of the fall of Adam and Eve (see Genesis 3:1). In the Hebrew language the creature is called a nahash, a viper, from which derives the noun for copper or brass (nehosheth), also used as an adjective denoting the "brass" serpent that Moses erected on a pole in the wilderness for the protection and healing of the Israelites (see Numbers 21:4-9).
On the one hand, the nahash in Genesis is clearly symbolic of evil, even the evil one (Satan), precisely because the serpent was in league with the devil, promoting the cause of the adversary and acting as his agent to bring about the fall (see Moses 4:5-31). On the other hand, when used by Moses under God's inspiration, the image of the nahash or, more precisely, the nahash nehosheth (brass serpent), became the agent of life and salvation for God's covenant people.
When Moses and Aaron went before the pharaoh they did exactly as the Lord had commanded. Their staff became a snake, which in the Hebrew text is denoted by two different terms, one of which is the very same word used earlier in Genesis to describe Eve's tempter, nahash (see Exodus 7:9, 10, 15). Either through sleight of hand, or by demonic power, Pharaoh's magicians were able to duplicate the action and turn their staffs into serpents as well. In what might be viewed as a quintessential showdown between God and the devil, the serpent of Jehovah swallowed up the serpents of Pharaoh as the God of Israel demonstrated his omnipotent supremacy (see Exodus 7:10-13). This scene dramatically illustrates the duality of serpent imagery in the scriptures.
In view of this dual symbolism, Skinner asks, But what of the origins of the serpent image as a symbol for Christ? And if the serpent was originally a legitimate emblem of the coming Messiah, how and why did Lucifer come to usurp the serpent symbol? In a roundabout way, the Prophet Joseph Smith may have provided a clue regarding the origins of serpent imagery as a symbol for Christ and why Satan appropriated it for his own. When speaking of the dove as an identifying symbol of the Holy Ghost, Joseph Smith said, "The sign of the dove was instituted before the creation of the world, a witness for the Holy Ghost, and the devil cannot come in the sign of a dove."
The implication of this statement is that other signs, symbols, and tokens were also instituted in premortality to represent deity, but the one that Satan absolutely could not imitate was the dove. However, as the preeminent counterfeiter and deceiver, Satan could and does usurp these other signs and symbols properly reserved for God in order to try to legitimize his false identity as a god. This is why Satan chose to use the sign of the serpent as the best means of deceiving Eve as well as her posterity from that moment on.
It seems quite plausible that like the sign of the dove, the sign of the serpent was instituted in premortality as a symbol of deity, particularly of Jehovah (see Exodus 4:1-5; 7:10-13; and Numbers 21:5-9) and later on as a symbol of Jehovah-come-to-earth, or in other words Jesus Christ (see John 3:14-15), the true God of life and salvation. It also seems plausible that both the signs of the dove and the serpent (as specific symbols of the true and living Lord) were made known to God's children in mortality sometime in the distant past. It is interesting to note that at the archaeological site in the Holy Land where most of the cultic objects bearing serpent imagery have been found (Beth-shan), the serpents are usually displayed in association with doves. In addition to the smaller religious objects that display the serpent-dove motif, each of the two Iron Age I temples at Beth-shan display the serpent-dove decoration. A fragment of the relief from the southern temple depicts deities standing and holding doves, while serpents wind upward with their heads almost touching the feet of the deities. In the northern temple, doves sit near the feet of deities as serpents glide towards the doves.
Over time the symbolic importance of the dove seems to have been lost altogether, while the symbol of the serpent was usurped by Satan, and then, over time, its true meaning became corrupted and diffused through many cultures over the ages. However, enough faint glimpses and echoes of its original and intended association with Christ exist to enable us to make significant connection to the truth as we engage in cross-cultural and historical studies. [Andrew C. Skinner, "Savior, Satan, and Serpent," in The Disciple As Scholar: Essays on Scripture and the Ancient World in Honor of Richard Lloyd Anderson, pp. 371, 373, 380-82]