1) Snakes played an important religious role in ancient Egypt and were depicted widely in art and iconography. When Moses was in Egypt, snake imagery would have been everywhere.
2) Some scholars propose that the Levite tribe, including Moses and Aaron, may have originated as Egyptian priests who followed Moses out of Egypt and had connections to snake handling and worship. References to snakes in the Bible may relate to this.
3) In the Bible, Moses was instructed by God to make a copper snake idol to cure snakebites, contradicting idol worship bans. This later developed into a snake cult in Jerusalem until being destroyed centuries later. Ancient Near Eastern snake cults and worship were common.