This towering figure of Orthodox spiritual life and teaching, the boast of Thessaloniki and spokesman for the Holy Mountain of Athos, is well known to students of Orthodox theology for his defense of the Hesychasts and exposition of the teaching of the Fathers on the Divine Energies and Theosis. What is not known, and with regard to which there is often great ignorance, even among Orthodox theologians in the West, is that the great hesychast was also a great defender of the Faith and Dogma of the Holy Trinity and a strident polemicist against the heresy of the filioque.

Now the divine wisdom of the theologian of Grace applied and embraced by the Church for more than half a millennium is available in the English language for all lovers of the Holy Trinity to be edified and enlightened. For the first time, St. Gregory's masterpiece, Apodictic Treatises on the Procession of the Holy Spirit, is available in English.

"Having returned again to the queen of cities, he published his treatise in two books against the Latins on the procession of the Holy Spirit in a wonderful way. This treatise was something original and extraordinary; our Church had never seen anything like it before on the subject. Indeed, to tell the truth, without any dissemblance or pretense, it was such as to make all the treatises against the Latins before this one look like childish games and mere semblances of dialectical argument."

• St. Philotheos Kokkinos, excerpt from Life of St. Gregory Palamas