Why should people who have witnessed so spectacular a display of the grace and power of God slip so easily into muttering and complaining and slide so gracelessly into listless disobedience? The answer lies in the fact that many of them see God as existing to serve them. He served them in the Exodus; he served them when he provided clean water. Now he must serve not only their needs but their appetites. Otherwise they are entirely prepared to abandon him. While Moses has been insisting to Pharaoh that the people needed to retreat into the desert in order to serve and worship God, the people themselves think God exists to serve them.
The fundamental question is, “Who is the real God?” New covenant believers face the same choice (1 Cor. 10:10).
–D. A. Carson, For the Love of God: A Daily Devotional for Discovering the Riches of God’s Word
Carson’s daily devotional is also available online at The Gospel Coalition website.