In Exodus 15:22–27, Israel’s quick turn from praise to grumbling in the wilderness reveals the deeper danger of the Christian life: not external enemies, but the sinful tendency of the heart to doubt God’s goodness when trials come. Their bitter waters at Marah expose both the reality of suffering and the temptation to respond with grumbling rather than lament. Yet God provides a remedy when he shows Moses a tree that turns the bitter water sweet, pointing forward to the greater “tree” of the cross, where Christ entered our bitterness, bore our curse, and turned the waters of death and sorrow into sweetness for his people.