«A few years ago, Bertrand Russell wrote a book with a title exactly the opposite of mine: Why I am not a Christian. It is a lucid and ironic work with which I fundamentally agree. What happens is that, when talking about Christianity, he and I talk about different things": this is how this new investigation by José Antonio Marina begins. He then explores the mighty current of Christian experience, which has its origins in an enigmatic Jew who lived twenty centuries ago. The followers of Jesus of Nazareth had to face the complex Hellenistic world, and choose between a "gnostic", philosophical interpretation, and a moral interpretation; between a charismatic conception and an institutional one. Part of our culture derives from these decisions.

Why investigate this matter now? Marina responds: «A philosopher has to face the essential issues of reality and also of his culture, and it seems evident that, in a Christian civilization like ours, knowing what to expect regarding the character to whom reference is constantly made is inevitable. .» Should we say a respectful but definitive goodbye to Jesus? And if not, why do we invite you to stay? There are several alternatives: as an incarnation of God, as a religious genius, as a literary invention, as an abstract revolutionary slogan.

This book is also a theory about truth. We suffer from an epidemic of credulity and fundamentalism, and religions have become a problem. We must demand that they clearly present their credentials to the world. What are they, where do they come from, where do they get their supposed reliability? Every preacher inevitably proclaims more certainties than he has. And not because of ill will, but perhaps on the contrary, because of the dangerous dynamism of good intentions. Marina distinguishes the domain of universal truths—science and ethics—from the domain of private truths, among which is religion. He does not deny their veracity, but maintains that when faced with universal truths, they must yield to them. In this way, religions, inevitably confronted dogmatically, could be reconciled on an ethical level.

The last chapter talks about the private truths of the world of J. A. Marina, and answers the question: why am I a Christian?