In the 3rd and 4th centuries CE, thousands of Christians fled the cities of Egypt, Palestine and Syria for the desert — seeking in solitude and silence the direct experience of God that they felt had been lost as Christianity became the official religion of the Roman Empire. The Desert Fathers and Mothers (Ammas) who emerged from this movement produced the first systematic account of the psychology of contemplative practice — the Philokalia (love of beauty/love of good), compiled in the 18th century from their writings, remains one of the foundational texts of Christian spirituality.
Their central concern was the purification of the nous (the spiritual intellect, the deepest level of human consciousness) from the passions (logismoi — compulsive thoughts and desires) that obscure its natural orientation toward God. The method was a combination of ascetic practice, watchfulness (nepsis) over the movements of the mind, and the repetition of the Jesus Prayer ("Lord Jesus Christ, Son of God, have mercy on me, a sinner") — the seed of the hesychast tradition.