In the fourteenth century a controversy arose in the Eastern empire between the Eastern Orthodox Theologian Gregory Palamas and a philosopher and monk from Calabria in southern Italy by the name of Barlaam. Barlaam was working on the problem of union between the Roman and Byzantine churches in the 1330s and actually acted as the representative of the Orthodox church. In his discussions, in which he repudiated the use of filioque (the addition to the Creed of the Holy Spirit proceeding from the Father and the Son), he argued for the unknowable and unapproachable nature of God. Gregory did not take kindly to what he perceived to be agnostic tendencies in Barlaam's thought, and he wrote a treatise about the procession of the Holy Spirit. However, it was particularly Barlaam's later attack on the hesychasts, a certain group of Orthodox monks, that led to a bitter debate between Gregory and Barlaam. Several basic issues were involved, centering on man's knowledge of God. The ideas that were defined in the debate by Palamas became crucial for the future of Eastern Orthodox thought.
Saint Gregory Palamas (1296-1359) was a monk of Mount Athos in Greece and later the Archbishop of Thessalonica known as a preeminent theologian of Hesychasm. He is venerated as a Saint in the Eastern Orthodox Church. Though he is not widely venerated in the Roman Catholic Church he is recognised as a saint. The second Sunday of the Great Lent is called the Sunday of Gregory Palamas in those Churches that commemorate him according to the Byzantine Rite. Some of his writings are collected in the Philokalia, a highly regarded book in the Eastern Orthodox Church. Palamas is perhaps most well-known for his central role in the defense of the doctrine of Hesychasm, which was upheld in 1351 at the Council of Blachernae.
Probably one of the best books I have ever read. The conclusion points this out, but you need to check the back of the book for citations. Palamas misquotes people a few times—usually mistaking the Cappadocians for St. Maximus—but it is important to remember, as the intro points out, Palamas is going almost entirely from memory. This book shows the untenable position of created grace–created grace=created God—and how the church fathers believed the theophanies were actually Jesus, not created. This is best shown by the transfiguration, the Cappadocians believed this was truly God's eternal glroy, yet in so many other passages they talk about the unkowablitiy of God. And thus, this book shows the Cappadocians and others believed in the essence/energy distinction as this is the only way to reconcile the disciples seeing Jesus' divinity in his eternal glory, yet also not being able to know God.