Whenever the question of “how” is raised in the early Christian writings, the answer comes back: by the Spirit. The Spirit who brooded over the waters of chaos, the Spirit who indwelt Jesus so richly that it became known as the Spirit of Jesus: this Spirit, already present within Jesus’ followers as the first fruits, the down payment, the guarantee of what is to come, is not only the beginning of the future life, even in the present time, but also the energizing power through which the final transformation will take place. The early creed spoke of “the Holy Spirit, the Lord and giver of life.” That is exactly true in the New Testament.
---Surprised by Hope: Rethinking Heaven, the Resurrection, and the Mission of the Church, by N.T. Wright (New York: Harper Collins, 2008. Page 163)