The nation of Israel will be the ones to preserve the Revelation of the true God and learn to walk depending on Him.

............On the third day of the journey, they arrive at Marah where the water was bitter.

.......................They were used to drinking the sweet water of the Nile, but acting childishly, they are disappointed and complaining against Moses.
Read Exodus 15:22-26

..................................God, proving His care for them, makes the bitter waters sweet.