The end of the chapter has a short story about the bitter waters of Marah. The people head for the wilderness of the wall—perhaps some Egyptian border fortification. When they’re running out of water, they come on water they cannot drink. Bitter, bitter, bitter, bitter, you read in Hebrew, which seems to be an implied superlative. Do they feel mocked by the circumstances? They murmur.
Of all the things there are to find in the wilderness, the Lord shows Moses a tree. Wood and water is how the plagues on Egypt began; Aaron took the rod and struck the Nile, and as a result the Egyptians had to dig around for water. This is why the Lord says he will put none of the disease on them that he put in the Egyptians. He does the reverse, he makes the water potable.
And it is a warning, so that nobody thinks that God chose Israel because they were slightly better than the Egyptians, that they were less likely to oppress other people the way the Egyptians oppressed them. If you think back to the time of Abraham and Sarah, you will remember Hagar the Egyptian slave. God is saying to the people here in Exodus 15 that they are no better than any others, that none who are chosen are better, but they are chosen because he is the Lord their healer. Unlike Pharaoh, there is mercy with the Lord.
Origen of Alexandria, who was tortured for his faith and refused to deny the Lord, speaks of how the wood of the Gospel makes the bitter waters of the law sweet. Isn’t that a good picture of the way it ought to work? Who loves the law thinking of it merely as a series of prohibitions? Who says, O how I love thy law as something that simply forbids and restricts and curtails? But when the law is a revelation of God’s character, when we understand that God when he forbids adultery does it because he is faithful, because he loves faithfulness, because he is faithful even to the unfaithful, because he is telling us about Christ, then we taste the sweetness of those waters.
Of all the things to show up in a wilderness, not a bush, not a bleached skull, not a cactus or a tumbleweed, but a tree. Sometimes a tree is just a tree. Still, is it any coincidence when everything wrong with the human race beings at a tree, and everything restored again takes place at a tree, that what Moses sees when he cries out to the Lord in the wilderness is a tree?