From: E.G. White

Trapped against the sea, the isrealites faced the Egyptian army sweeping in for the kill. The Israelites thought they were doomed. After watching God's powerful hand deliver them from Egypt, their only response was fear, whining and despair. Where was their trust in God? Israel had to learn from repeated experience that God was able to provide for them. God has preserved these examples in the bible so that we can learn to trust Him the first time. By focusing on God's faithfulness, in the past we can face cries with confidence rather than with fear and complaining.
This is the first instance of grumbling and complaining by the isrealites. Grumbling would become a great a major problem for the people on this journey. Their lack of faith in God is startling. Yet how often we do the same thing. Complaining over inconveniences and discomforts. The Israelites were about to learn some tough lessons. Had they trusted God, they would have been spared much grief.
The people were hostile and despairing, but Moses encouraged them to watch the Wonderful way God would rescue them. Moses had a positive attitude! When it looked as if they were trapped, Moses called upon God to intervene. We may not be chased by an army, but may still feel trapped. Instead of giving into despair, we must adopt Moses' attitude to "STAND STILL AND WATCH THE LORD RESCUE US."