DEIFICATION IS POSSIBLE THROUGH THE UNCREATED ENERGIES OF GOD
Let us mention a somewhat relevant example from things human. If we grasp a bare electric wire, we will die. However, if we connect a lamp to that wire, we are illuminated. We see, enjoy, and are assisted by the energy of electric current, but we are not able to grasp its essence. Let us say that something similar happens with the uncreated energy of God.
If we were able to unite with the essence of God, we too would become gods in essence. In other words everything would become a god, and there would be confusion so that, nothing would be essentially a god. In a few words, this is what they believe in the Oriental religions, e.g. in Hinduism, where the god is not a personal existence but an indistinct power dispersed through all the world, in men, in animals, and in objects (Pantheism).
Again, if God had only the divine essence – of which we cannot partake – and did not have His energies, He would remain a self-sufficient god, closed within himself and unable to commune with his creatures.
God, according to the Orthodox theological view, is One in a Trinity and a Trinity in One. As St. Maximus the Confessor, St. Dionysius the Areopagite, and other holy Fathers repeatedly say, God is filled with a divine love, a divine eros for His creatures. Because of this infinite and ecstatic love of His, He comes out of Himself and seeks to unite with them. This is expressed and realised by means of His energy or, better, His energies.
With these, His uncreated energies, God created the world and continues to preserve it. He gives essence and substance to our world through His essence-creating energies. He is present in nature and preserves the universe with His preserving energies; He illuminates man with His illuminating energies; He sanctifies him with His sanctifying energies. Finally, He deifies him with His deifying energies. Thus, through his uncreated energies, holy God enters nature, the world, history, and men's lives.
The energies of God are divine energies. They too are God, but without being His essence. They are God, and therefore they can deify man. If the energies of God were not divine and uncreated, they would not be God and so they would not be able to deify us, to unite us with God. There would be an unbridgeable distance between God and men. But by virtue of God having divine energies, and by uniting with us by these energies, we are able to commune with Him and to unite with His Grace without becoming identical with God, as would happen if we united with His essence.
So, we unite with God through His uncreated energies, and not through His essence. This is the mystery of our Orthodox faith and life.
Western heretics cannot accept this. Being rationalist, they do not discern between the essence and the energy of God, so, they say that God is only essence. And for this reason they cannot speak about man's deification (gr. theosis). Because, according to them, how could man be deified when they do not accept that the divine energies are uncreated, but regard them as created? And how could something created, i.e., something outside God, deify created man?
In order not to fall into pantheism, they do not speak at all about deification (gr. theosis). What then, according to them, remains as the purpose of man's life? Simply moral improvement. In other words, since man cannot be deified by means of divine Grace, the divine energies, what purpose does his life have? Only that he becomes morally better. But moral perfection is not enough for man. It is not enough for us simply to become better than before, to perform moral deeds. We have as our final aim to unite with holy God Himself. This is the purpose of the creation of the universe. This is what we desire. This is our joy, our happiness, and our fulfillment.
The psyche of man, who is created in the image and likeness of God, yearns for God and desires union with Him. No matter how moral, how good man may be, no matter how many good deeds he may perform, if he does not find God, if he does not unite with Him, he finds no rest. Because holy God Himself placed within him this holy thirst, the divine eros, the desire for union with Him, for deification (gr. theosis). He has in himself the erotic power, which he receives from his Creator, in order to love truly, strongly, selflessly, just as his holy Creator falls in love with His world, with His creatures. This is so that with this holy erotic impetus and loving power, he falls in love with God. If man did not have the image of God in himself, he would not be able to seek its prototype. Each of us is an image of God, and God is our prototype. The image seeks the prototype, and only when it finds it does it find rest.
In the fourteenth century, there was a great upheaval in the Church which was provoked by a Western monk, Barlaam. He heard that Athonite monks talked about deification (gr. theosis). He was informed that, after much struggle, cleansing of the passions, and much prayer, they became worthy to unite with God, to have experience of God, to see God. He heard that they saw the uncreated light which the holy Apostles had seen during the Transfiguration of our Saviour Christ on Mount Tabor.
But, having the Western, heretical, rationalistic spirit, Barlaam was unable to perceive the authenticity of these divine experiences of the humble monks, and so, he began to accuse the Athonite monks as though it was they who were deluded, heretical, and idolatrous. In other words he was saying that it was impossible for someone to see the Grace of God, because he knew nothing about the distinction between the essence and the uncreated energy of God.
Then, God's Grace brought out a great and enlightened teacher of our Church, the Athonite St. Gregory Palamas, Archbishop of Thessaloniki. With much wisdom and enlightenment from God, but also from his personal experience, he said and wrote much which taught, in accordance with the Holy Scriptures and the Holy Tradition of the Church, that the light of God's Grace is uncreated; that it is a divine energy. That, in fact, deified men see this light as the ultimate, the highest experience of deification (gr. theosis), and that they are seen within this light of God. This is the glory of God, His splendour, the light of Mount Tabor, the light of Christ's Resurrection and of Pentecost, and the bright cloud of the Old Testament. It is the real uncreated light of God, and not symbolic as Barlaam, and others like him, believed in their delusion.
Subsequently, in three great Synods at Constantinople, the whole Church justified St. Gregory Palamas, declaring that life in Christ is not simply the moral edification of man, but deification (gr. theosis), and that this means participation in God’s glory, a vision of God, of His Grace and His uncreated light.
We owe great gratitude to Saint Gregory Palamas, because, with the illumination he received from God, with his experience and his theology, he bequethed to us the teaching and eternal experience of the Church concerning the deification (gr. theosis) of man. A Christian is not a Christian simply because he is able to talk about God. He is a Christian because he is able to have experience of God. And just as, when you really love someone and converse with him, you feel his presence, and you enjoy his presence, so it happens in man's communion with God: there exists not a simply external relationship, but a mystical union of God and man in the Holy Spirit.
Even now, Westerners consider the divine Grace, or the energy of God, as something created. Unfortunately, this also is one of the many differences which must be seriously taken into consideration in theological dialogue with the Roman Catholics. It is not only the filioque, the primacy of authority, and the ‘infallibility’ of the Pope which are basic differences between the Orthodox Church and the Papists. It is also the above. If the Roman Catholics do not accept that the Grace of God is uncreated, we cannot unite with them even if they accept all the other points. For who is able to effect deification (gr. theosis), if divine Grace is a creation and not an uncreated energy of the All-Holy Spirit?
Source-http://www.greekorthodoxchurch.org