The Mekhilta presents two sharply different readings of the verse "And the people caviled against Moses, saying: What shall we drink?" Rabbi Yehoshua takes the generous view: the people should have consulted their leader first. Moses was right there. He had just led them through the Red Sea. He had a direct line to God. If anyone could solve a water shortage, it was Moses. Instead of asking for help, they confronted him with accusations.
Rabbi Yehoshua's reading treats the people's complaint as a failure of process, not faith. They had the right concern — thirst is legitimate — but they expressed it the wrong way. They should have sought counsel from their leader rather than attacking him.
Rabbi Eliezer Hamodai takes a much harsher view. Israel was "conversant" in complaining — meaning they were practiced at it, skilled at it, habitual complainers who had developed the art of protest into a reflex. And their complaints were not limited to Moses. They complained against the Omnipotent Himself.
The word "conversant" is devastating. It implies that the murmuring at Marah was not a one-time lapse of faith under extreme duress. It was an established pattern of behavior — a national tendency to respond to difficulty with accusation rather than prayer, with confrontation rather than trust. The people who had just sung at the sea were already complaining before the echo of their song had faded.