Final answer:
Moses and Aaron were barred from entering Canaan due to their disobedience at Meribah, where they struck a rock to bring forth water instead of speaking to it as God had commanded, displaying a lack of faith and contravening God's instructions.
Step-by-step explanation:
According to the Hebrew Bible, Moses and Aaron were not allowed to enter Canaan, the Promised Land, because of an incident at Meribah, recorded in Numbers 20:1-13. Here, the Israelites quarreled with Moses and expressed their discontent due to the lack of water. Moses and Aaron sought the Lord's guidance, and God commanded Moses to speak to a rock to bring forth water. Instead of speaking to the rock as commanded, Moses struck it twice with his staff. Water did indeed come forth, but the manner of Moses’ and Aaron's actions displayed a lack of faith in God's word and a disobedient spirit. As a result, God told Moses and Aaron that they would not bring the congregation into the land He had given them. This was God's punishment for their disobedience and lack of trust.
In the biblical narrative, this act was seen as a significant transgression because it went against the commandments given by God and demonstrated a failure to uphold the sanctity and authority of God before the people. Consequently, leadership passed to Joshua, who led the Israelites into Canaan after the death of Moses and Aaron.