"Stories show a character changing, at the least, and transforming at the most profound. This potential for growth reflects meaning. Meaning reflects truth. The thematic significance of a story shows what all the words in each individual scene add up to. ... The thematic significance of a story is a statement the story illustrates as truth."
Alderson goes on to point out that this theme needs to be refined into a single sentence or two, and warns that this takes some work.
It's basically the LESSON the protagonist learns as a result of the journey. You need to know what it is. You need to boil it down into a few words. This is a pain, but it's got to be done.
Alderson identifies the theme of TO KILL A MOCKINGBIRD as: "You never really know another person until you climb into his skin and walk around in it." This is what Scout learns.
[Here I shared with my friend the Thematic Statement of my novel Jihadi -- what my protagonist Thelonius Liddell learns from the journey -- which you can get when you read the book.]
From there, you can create what I call a Thematic Cloud that connects to your Theme Statement. (Alderson calls this grouping of words a Thematic Significance Bubble Template. I like Thematic Cloud better.) These are basically Lessons Each Individual Scene Must Touch On. They can touch on more than one, if necessary, but they have touch on at least one. So for my novel Jihadi the Thematic Cloud looks like this:
Just a little something for you to gnaw on in your spare time. You might or might not decide make a Thematic Cloud, but I bet you need a Thematic Statement that shows the lesson your protagonist learns from all his trouble.