The rod Aaron used to demonstrate to the Pharaoh that the God of the Hebrews was Lord. It became a snake when cast down (Exodus 7:8-13) and brought about the first three plagues (Exodus 7:19-20; Exodus 8:5-7; Exodus 8:16-19). This rod was also used to strike the rocks at Horeb and Kadesh to bring forth water (Exodus 17:1-7; Numbers 20:7-11).
The rebellion of Korah (Numbers 16:1-50) made it necessary to determine who would be eligible to come before God in the tabernacle as priests (see Numbers 17:1-11). According to Hebrews 9:4, the rod was kept in the ark of the covenant.