Hesychia means “stillness” or “quiet.” The hesychast tradition — developed on Mount Athos and systematized by gregory-palamas in the 14th century — teaches that through the The Jesus Prayer and inner watchfulness (nepsis), one can become aware of the uncreated divine light that disciples saw at the Transfiguration.
Palamas defended this against scholastic critique by distinguishing God’s unknowable essence from God’s knowable energies — a distinction that became central to Orthodox theology and one of the lines of separation from Western Christianity.