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.
This had an important result: the life of the mind was itself elevated by Paul from a secondary social activity, for those with the leisure to muse and ponder life’s tricky questions, to a primary socio-cultural activity for all the Messiah’s people. The interesting question of whether one thinks oneself into a new way of acting or acts oneself into a new way of thinking will, I suspect, continue to tease those who try to answer it (not least because it is of course reflexive: should you answer it by thinking or by acting?).
N. T. Wright, Paul and the Faithfulness of God, vol. 4, Christian Origins and the Question of God (Minneapolis: Fortress Press, 2013), 27.
For the early Christians, philosophy became a way of life.