Equating the serpent with Satan may have its roots in Egyptian mythology. Apep was the serpent of the underworld and also the enemy of Ra (or Re), an Egyption sun god and creator deity. Since the two groups are quite close geographically, it would make sense for Judaism, and later by proxy Christianity to borrow heavily from this older tradition. The term Satan may also have its roots in Egypt, since Set (also pronounce Seteh, Seth, among others) was worshiped in ancient "Lower Egypt," which is actually in the North, close to the land of the Hebrews. As it is documented these groups did not get along. Satan may be a slanderous form of the Egyptian god's name or perhaps the result of different dialects. Set was also the enemy of Horus, another sun god who was part of the ruling triad of Ra, Osirus, and Horus. The latter is often equated with Christ due to his being considered son, brother, and different incarnation of Ra, and the reincarnated form of Osirus, (Egyptian mythology is convoluted... long story short a son figure and key link in what could be considered a trinity... but that may be a stretch) death & rebirth and the veneration and worship of his mother, Nepthys, in addition to many other similarities. This is all speculation of course, but certainly interesting to think about.
Noah
