St. Gregory was born in a.d. 1296 in a noble family in Constantinople at the time of the Emperor Andronikos II Palaeologos, who took care of his education when St. Gregory’s father died early. St. Gregory was gifted and learned philosophy well, but left the world at twenty to enter a monastery on Mount Athos, where he deeply learned the great art of Hesychast Prayer in obedience to his elders, and matured in monastic and spiritual life.
The Calabrian monk Barlaam at that time tried to spread the erroneous ideas of Thomas Aquinas into Orthodoxy, with its emphasis on rational thought and education as the means to know God. This was contrary to 1,300 years of Orthodox spiritual tradition, which taught that we can know God directly through prayer and ascetic life, not from imperfect intellectual contemplation. St. Gregory became the champion for the defense of Hesychasm against such heresy, was the great theologian of the Essence and Energies of God, and was vindicated by two local councils of the church about a.d. 1350. St. Gregory later became the Bishop of Thessalonica, and is greatly venerated as a Champion of the Faith.