Then Moses led Israel onward from the Red Sea, and they went into the wilderness of Shur; they went three days (33 miles) in the wilderness and found no water...The people murmured against Moses, saying, what shall we drink (Exodus 15:22,24 Amp)?
God is looking for a people of faith who will know him enough to trust him under any circumstances - to know that he is there and will come through. He just wants a people whom he can truly call his. People with a pure heart towards him ? people who love him and obey him not only for what he can do for them or because he will bless them.
He wants a people whose hearts are turned solely towards him alone - regardless of the circumstances. God wants a people. Even from the beginning when he had the entire angelic realm in place, he still wanted a people who wanted him, and loved him and trusted him.
It is a law of life. We must be tested on what we think we know, on the things we think we have learned. It is a principle that mankind knows and has followed over the years. We give tests in schools, colleges, and we even test each other's love and friendship. It is a principle generated by God himself. He wants us to learn to embrace him, to trust him in every situation: to believe in him and trust him no matter what.
That is why he allowed the Israelites to go three days without water. He was trying to let them know him, to show them what he is like and how he acts. He wanted them to know that he wouldn't let them die of hunger or thirst. He wanted them to love and trust him. He had been trying to show them the same thing throughout the period of the plagues in Egypt and even when Pharaoh and the Egyptians pursued them into the Red Sea. He never failed them. He came through in the nick of time - his time - because he is a faithful God and patient. But they did not trust him.
God is trying to make you know him and learn to trust him implicitly, so that he in turn can trust you. So that you can become a man or woman in whom he can confide in, and open his heart to, like Moses and Abraham and the prophets. Can he trust you to be faithful to him at all times, in every situation?