I have puzzled and thought. There must be five transformative books in my collection. I can think of books that I've loved, books that I've cried over, books that I've waded through. I have a pile of books that I would like to read, but haven't yet. But books that have changed me?
When I was studying medicine, I read The Audacity to Believe by Sheila Cassidy. She tells the story of going to Chile and working as a doctor. She was a Catholic follower of Jesus and she tried to live out her faith. I found this really challenging and it influenced how I wanted to work in the future.
The Bible itself has changed me, but I want to highlight the effect of the Psalms on me. I did a course about the Psalms once and read it through a few times. I always found that reading a book and talking about it (eg. in high-school English) gave me a deeper love of it. This happened with the Psalms. Suddenly the words were passionate and spoke to me face-to-face. I began to understand why the word of God had been described as being sweeter than honey and purer than gold, through reading the Psalms.