What was it that they did to displease God?
AMP - 24 Aaron shall be gathered to his people. For he shall not enter the land which I have given to the Israelites, because you both rebelled against My instructions at the waters of Meribah.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
The disobedience came from the striking of the rock. When God told him to say something ...( to make sound speech) to the rock Somit would yield water. This in return would give the power of God's word the glory and not the rod or Moses.
Also, Moses' action implied that Christ would need to 'die twice', that being struck once was not sufficient. God asked Him once before, in a prior incident, to strike the rock; that is likely why Moses thought striking it was needed later, leaning on his own understanding vs. obeying God.