What does the Bible say about speaking against God's appointed leaders?

In Numbers 12, Miriam and Aaron spoke against Moses due to his marriage to an Ethiopian woman. God's response highlights the seriousness of speaking against His appointed leaders, showing that such actions are direct opposition to God's authority. The Lord emphasized Moses’ unique place among His prophets and expressed His displeasure at their rebellion. This incident illustrates that speaking against God's ordinations is not merely criticism but is fundamentally against God Himself, which carries severe consequences.