Quakers are people who belong to the Religious Society of Friends, a historically Protestant Christian set of denominations. Members of these movements are generally united by a belief in each human's ability to experience the light within or "answering that of God in every one". Some profess a priesthood of all believers inspired by the First Epistle of Peter. They include those with evangelical, holiness, liberal, and traditional Quaker understandings of Christianity. There are also Nontheist Quakers, whose spiritual practice does not rely on the existence of God. To differing extents, the Friends avoid creeds and hierarchical structures. In 2017, there were an estimated 377,557 adult Quakers, 49% of them in Africa.

Christian perfection is the name given to the process or the event of achieving spiritual maturity or perfection; it is a theological concept that exists within many denominations of Christianity. The ultimate goal of this process is union with God characterized by pure love of God and other people as well as personal holiness or sanctification. Other terms used for this or similar concepts include entire sanctification, perfect love, the baptism with the Holy Spirit, the indwelling of the Holy Spirit, baptism by fire, the second blessing, and the second work of grace.