The Fathers teach that we know God through His energies. What are energies?
Christos Yannaras describes energies as,
"Those potentials of nature or essence to make known the hypostasis and it's existence, and to make it known and participable."
Let's think about this in terms of our relationship with another person. What is it that distinguishes one person from another? Isn't it their energies? It is through a direct encounter with another person where we experience their energies that we are able to know their unique otherness. It is in this way that we know them in truth. Any abstract knowledge that comes from what they have written or what others have written about them is only indirect knowledge. By examining their work, their art, or anything they have made we only have limited knowledge of them. To know their otherness we must share in their energies involved in a personal and face to face relationship. When we meet them, hear them speak, see their look, experience how they act we can say we know them directly by participating in their energies. Otherwise, we can only say we know them indirectly.
This is also true with God. It is through His energies that we know Him as distinct from His creation. Through the reading of Scripture or our study of His creation we can only know Him indirectly. To know him in truth, like an encounter with another person, we must participate in His energies. This requires a relationship where we share in His uncreated divine energies. This is in a direct relationship with God, just like Peter, Paul and the other Apostles, the saints and elders who know His uncreated divine light experienced, that we too can know Him.
To know God directly is to "become partakers of his divine energies." (2Peter 1:4) This needs to be our aim in life. Our salvation demands much more than a declaration of faith or a knowledge of Scripture and more than theorizing or knowledge of any abstract dogma about reality. These only give us indirect knowledge of God. Our salvation requires a transformation that comes from the sharing, participating in, a direct encounter with the uncreated energies of God, becoming one with His energies. This is what we call Theosis. This is how we know God in truth through knowing His energies.
Reference: Elements of Faith, Christos Yannaras, pp 37 -46
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