What is the strongest theme in the story?

One of the strongest themes is coming of age, the step from childhood to adulthood.

That violent, crazy act was the last act of childhood. For as I gazed at the immobile face with the sad, weary eyes, I gazed upon a kind of reality which
is hidden to childhood. The witch was no longer a witch but only a broken old woman who had dared to create beauty in the midst of ugliness and sterility.

The years have put words to the things I knew in that moment, and as I look back upon it, I know that that moment marked the end of innocence.