Gregory Palamas

Byzantine monk, theologian, and Archbishop of Thessaloniki; the foremost theological defender of hesychasm — the Eastern Orthodox mystical tradition of contemplative prayer aimed at direct experience of the divine light; formulated the essence-energies distinction to defend the possibility of genuine human participation in God's life.

His essence-energies distinction — that while God's essence remains forever unknowable, His uncreated energies are genuinely available to human participation — resolved the central tension in Eastern Christian thought between apophaticism and theosis; became the cornerstone of all subsequent Eastern Orthodox theology.