The Israelites are on their way to Mount Sinai, but they are not satisfied with being saved from the bondage of slavery to Egypt. They must have expected their lives to be perfect, but life has challenges. The wilderness becomes a place of testing and trials. First, the water was bitter; then they were hungry and wanted food. God supplied both those needs abundantly. He even comes in His glory to his people.
Now as they are being led by God, they arrive at a place without water and grumbling occurs again.