The Children of Israel are not just allowed to go out of Egypt, they are ejected. Out of consideration for their morale, they are taken a roundabout route so as to avoid facing armed opposition on the short coastal journey to Israel. Their apparent confusion encourages Pharaoh to recover his arrogance and give chase. The Israelites are trapped with their backs to the sea as the enemy advances. Miraculously, Moses leads them through the Red Sea. The Egyptians are drowned. Safely on the other side, they break into song to celebrate.
You might have thought that having seen what happened to the Egyptians in Egypt, and again at the Red Sea, there would not be one dissenting voice and everyone would be absolutely convinced of the existence and the power of God–yet immediately afterwards the complaints begin.
Three days without water is perhaps reasonable grounds. But why gang up against Moses instead of a reasoned discussion of the problem? Moses sweetens water for them at Marah, and at Eilim there are wells and date palms. But then the moaners start again, complaining about the food. One might have had some sympathy were it not for the fact that they said how wonderful it had been in Egypt. Nevertheless, down comes the manna, and whatever one might think about a daily diet of neutral sesame wafers, at least they were not dying of hunger. Yet once again the complaints start up against Moses over water.
Some apologists want to suggest that the mixed multitude hangers-on who joined the exodus were to blame, but the text implies a much wider groundswell of discontent. Isn’t it amazing? They experience the reality of God time after time and they still don’t get it. Times haven’t changed much for us Jews, have they? We are an ungrateful, moaning bunch of doubters who wouldn’t face reality even if it came and tapped us on the shoulder.