Chapter 15 records three different events, but it appears that the image of “water” draw comparison and contrast between them.
14:30 That day the LORD saved Israel from the hands of the Egyptians, and Israel saw the Egyptians lying dead on the shore. 31 And when the Israelites saw the mighty hand of the LORD displayed against the Egyptians, the people feared the LORD and put their trust in him and in Moses his servant. 15:1 Then … (Exod 14:30-31; 15:1)
The “then” in 15:1 tells that the verses following it are responses to what happened at the end of chapter 14. God splited the water in half to let Isralites to walk through but covered on Egyptians army who chased after Israelites. Moses didn’t take the credit. He gave glory to God and led all Israelites to response by singing a song. Miriam also response to lead all the women to follow. We need to give glory to God, not forgetting His salvation. We also need to learn leading other people to response to God’s salvation.
22 Then Moses led Israel from the Red Sea and they went into the Desert of Shur. For three days they traveled in the desert without finding water. 23 When they came to Marah, they could not drink its water because it was bitter. (That is why the place is called Marah.) (Exod 15:22-23)
The second place is named Marah, because it has bitter water. They could not find water for three days until they reach this place, but finally found that the water is not drinkable. From excitment to despair, they started to grumble. Just three days ago, they saw how God can control water, but now they grumble against Moses, without praying to God. Hardship sometimes is a kind of testing, we need to learn keeping our eyes on God, not environment or people around us. If we keep His words wholeheartedly, disasters won’t overtake us (8:25). As an example for us, Moses cried out to God in this difficult situation. God then revealed him a way to transform the water.
Then they came to Elim, where there were twelve springs and seventy palm trees, and they camped there near the water. (Exod 15:27)
The third place is Elim, where plenty of water is found. It is obvious an immediate contrast to Marah where they just left. God leads them to this place to enjoy His provision. But it could be another kind of testing to Israelites. On way to the Holy Land, Israelites grumbled most of the time. Elim is one of the rare places where Israelites did not complain. Elim is a comfort zone for them. The question is whether they would leave this nice place to where God lead them. They did only because they believed God have a place even better than this one for them. We need to learn to leave comfort zone and advance forward to receive the best God reserved for us.