Saint Gregory of Naziansus/ (328-390) The Theologian, sometimes called the minstrel of the Holy Trinity: "The divine nature [essence] surpasses intelligence, and though they may contemplate the Trinity, though they may receive the plenitude of His light [energy], human intellects cannot know God in His nature [essence]." (Oracle XXVIII, 4, PG.36, col.32)
St. Macarius the Great/ (c.330-389) He speaks of the fire of grace kindled by the Holy Spirit, making them burn like candles, but it no longer sheds its radiance in hearts that are darkened by passions (cf. Homilies 5, 8. PG.34, col.513B).
St. Dionysius the Areopagite/ (c. the end of the 5th to the beginning of the 6th century) He was quoted frequently by both Eastern and Western theologians, e.g., St. Gregory Palamas and St. Thomas Aquinas. Of all theologians, Dionysius is one who has stressed most the inaccessibility of God's divine essence. Yet, at the same time, he seems to be the one who has given countless names to the accessible attributes or energies of God (cf. Dionysius the Areopagite, The Divine Names and The Mystical Theology, pp.51-190)
St. Maximus the Confessor/ (c.580-662) "God is comprehensible in our contemplation of His attributes [or divine energies], but God is incomprehensible in our contemplation of His divine essence." (Cent. On Charity, IV, 7, trans. Pegon, Sources Chretiennes 9, p.153)
St. Symeon the New Theologian/ (949-1022) He talks about God's divine energy in Heaven: "The grace [light or energy] of Christ's Holy Spirit will shine like a star upon the righteous and in the midst of them thou wilt shine, thou, O Inaccessible Sun [God in His divine essence]." (Sermon 27, trans. in Vie Spirituelle, no.27, 1931, p.309).
St. Gregory Palamas/
(1296-1359) "Like Dionysius, the Fathers apply to energies
the name of 'rays of divinity', penetrating the created universe.
St. Gregory Palamas calls them quite simply 'divinities', or 'uncreated
light', or 'grace'." (Vladimir Lossky, The Mystical Theology
of the Eastern Church, p.73)