The life of the mind in early Christianity
This is the best couple of paragraphs from N.T. Wright's massive two volume tome:
That is the point at which Paul found himself inventing and developing this new discipline we call, in retrospect, ‘Christian theology’. The radically new worldview in which he and his converts found themselves was bound to face the question ‘why’ at every corner, and in order to answer it, and to teach his churches to answer it for themselves, he had to speak of one particular God, and of the world, in a way nobody had done before.