I have never argued more with a book than the one that sits before me now. When I open my dog-eared copy of the Catechism of the Catholic Church, I see page after page covered in pencil marks. The comments, written almost 20 years ago, read like those of a stranger: someone trying to argue his way out of becoming a Catholic. As I flick through the book, with its yellowed and broken spine, I see expressions of bafflement and even outrage. I dismissed one section (83) as "Essentialised tradition". Next to another (107) I simply wrote "difficulties". But as the pages turn, there are fewer objections. I remember marvelling at the Catechism's elegant structure: its four parts – the Profession of Faith, the Celebration of the Christian Mystery, Life in Christ and Christian Prayer – serving as a firm foundation for the soaring tower of Catholic teaching. I was impressed that the book not only explained what Catholics believe, but also how to be a Catholic. I had expected it to be a dry-as-dust manual, but it had such zeal and beauty that my objections to Catholicism collapsed one by one, until none remained. It was only later that I discovered how controversial the Catechism had been within the Catholic Church. As Cardinal Christoph Schönborn explains in an interview marking the book's 25th anniversary, there were "violent discussions" over whether a universal Catechism was desirable or even possible. "The main argument of the opponents of this project," he recalls, "was: it is impossible to create a book of faith for the entire world – a Catechism for the whole world Church – today, in the face of the pluralism of cultures, theologies and narratives. This was the most massive counter-argument against the project. "I think Cardinal Ratzinger took this challenge very seriously. It was ultimately a question of a fundamental theological opinion: can faith today be formulated as one faith in a common form?" I am so grateful that Cardinal Schönborn, Cardinal Ratzinger and their colleagues persisted. If they hadn't, it's quite possible I wouldn't be a Catholic today.