In his brand new commentary, Victor Hamilton makes the following astute observation.
“Why the Lord brings his people out of Egypt is as important, if not more important, than how he delivers Israel from Egypt. If the book of Exodus is about the exodus event, then the book should be concluded by the end of chap. 14, or by 15:21 if one wants to include Miriam's and Moses’s lyrical response. But what is one to do with 15:22–40:38, all of which are postexodus events in the Exodus book?”