Psalms 81:6-7

God had told His people that He was freeing them from their bondage as slaves in Egypt. They had cried out to Him in their distress, and He answered them from heaven.

"To judge by this model, it is good to recall God’s answers with some sharpness of detail." [Note: Kidner, Psalms 73-150, p. 294.]

Then He tested them at the waters of Meribah to see if they would trust Him (Exodus 17:1-7), and in order to train them to do so.