This study is a historical investigation of the Christian spirituality of a Swedish Pentecostal author, pastor and Retreat leader, Peter Halldorf. His books from 1984 to 2019 were investigated, using three categories; doctrines (beliefs), practices and affections. The investigation reveals a considerable change over the years in Halldorf`s spirituality as evidenced in the texts. The investigation shows the persons and milieus that have had formative influence on Halldorf’s spirituality, chiefly Alexander Schmemann, Thomas Merton, Lev Gillet, Pope Francis, Matta-Al-Miskin, the Desert Fathers, early Christianity through Church Fathers, and especially the spirituality of Eastern Churches. Halldorf’s books are characterized by a desire for Bible centered discipleship and radical holiness for the ultimate purpose of Christian unity. The great Christian Tradition is very important in Peter Halldorf’s books and his spirituality