St. Gregory Palamas ca. 1296-1359
Three realities pertain to God: essence, energy, and the triad of divine hypostases. As we have seen, those privileged to be united to God so as to become one spirit with Him – as St Paul said, ‘He who cleaves to the Lord is one spirit with Him’ (1 Cor. 6:17) – are not united to God with respect to His essence, since all the theologians testify that with respect to His essence God suffers no participation. Moreover, the hypostatic union is fulfilled only in the case of the Logos, the God-man. Thus those privileged to attain union with God are united to Him with respect to His energy; and the ‘spirit’, according to which they who cleave to God are one with Him, is and is called the uncreated energy of the Holy Spirit, but not the essence of God, even though Barlaam and Akindynos may disagree. Thus God prophesied through His prophet saying, ‘I shall pour forth’, not ‘My Spirit’, but ‘of My Spirit upon the faithful’ (cf. Joel 2:28. LXX). (Topics of Natural and Theological Science and on the Moral and Ascetic Life: One Hundred and Fifty Texts 75)