Christian Mysticism refers to a wide variety of practices within Christianity that encourage believers to achieve a direct personal experience with God. This experience with God is not an emotional response but an encounter with God that is beyond intellectual and psychological understanding. The goal of this experience is to be transformed by being in union with God and Christ. Christian mysticism can be traced back to the earliest stages of Christianity, including the experiences of many of the early Desert Fathers in the 3rd and 4th centuries C.E. who would spend long periods of time in the desert in self-denial and prayer. Some of the most famous Christian mystics have included St. Teresa of Avila and St. John of the Cross in the 16th century. Many forms of Christian mysticism have included practices such as prayer and meditation, as well as other disciplines including fasting, self-denial, and service to others. These disciplines are typically meant to purify oneself before the mystical encounter. There has been a wide variety of responses to mysticism within Christianity. Some Christian mystics have been deemed heretics and expelled from the church while other churches have either tolerated it or embraced it to varying degrees.