Teaching on the sanctification of Christians using the difficult word "perfection" has been part of Christian spirituality through the centuries. The Church Fathers spoke of it and Augustine of Hippo particularly contributed his penetrating analysis of human motivation in terms of love. Medieval theologians such as Bernard of Clairvaux and Thomas Aquinas developed the tradition and wrote of levels or "degrees" of "perfection" in love. However, the doctrine has not fared well among Protestants. John Wesley was the one major Protestant leader who tried to blend this ancient tradition of...