Classical, creedal Christianity is reasonable because:
1) Theism (the belief that there is a supreme being of some kind) is a reasonable explanation for fine-tuning of the universe, the intuitive realm of objective moral values, and the universal phenomenon of transcendent longing.
2) A movement of invidividuals and groups grew quickly and unexpectly–against many opposing forces including embarrassment, social rejection, and open persecution–with a relatively unified, coherent, remarkably durable and reliable witness to the life and teachings of Jesus Christ.
3) The resulting meta-physical and philosophical frameworks have deep explanitory power in regards to the human condition, the problem of suffering, consistent morals and ethics, and living the good life.
4) My own experience of living in the story of Christianity has ignited faith, hope, and love in my own heart, and I continually see it doing the same in others–both in history and in the present.