A couple of thoughts which may (or may not) be helpful to folks in trying to understand theosis. I confess that I have no idea what it means to say that in divinization we share in the divine energies of the Trinity but not in the divine essence; but I understand why this distinction is made. If it were possible for us to actually possess the divine essence, we would in fact become divine hypostases, just as the Father, Son, and Holy Spirit are divine hypostases. Clearly neither Eastern nor Western Christianity wants to say this. In theosis, we do not cease to be creatures, though several of the Eastern Fathers are bold enough to declare that we in fact become uncreated by grace. I personally find the language of essence, energies, nature, and being unhelpful. I don’t know what these words really mean and I suspect most others don’t either. We toss them around easily enough, but the simple fact is that they point us to the mystery of God that surpasses anything we can understand.
The language is used to refer to our incorporation by grace into the inner relationships of the Father, Son, and Holy Spirit and by this incorporation we are radically transformed and transfigured. God is no longer external to us; in Christ we become internal to him, for we share in the divine Sonship of Christ and now live in the Holy Spirit. It’s all personal.
In his book God Matters Fr Herbert McCabe speaks of the difference between God loving a creature and God loving himself in his inner Trinitarian being. God’s love for creatures necessarily involves inequality. As Creator God can beneficently care for the creatures he has made; but precisely as creatures they cannot be loved, for real love is something that takes place between equals. In my judgment theosis is first and foremost about our incorporation to the Trinitarian family of the Triune God. God the Father, by grace, loves us with the same love that he loves his Son Jesus Christ. He gives himself over to us through the Holy Spirit and we in turn give ourselves over to him in the same Holy Spirit.
I’m also tempted to say forget about what it means to participate in the divine nature. Concentrate on what it means to be elevated into the intimate relationships between the Father, Son, and Holy Spirit and to share in this love between equals. And If we are loved as equals, they we are, in the way we have already qualified, gods by grace. As McCabe states:
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Personally I find this a helpful way to begin to think about theosis. There’s so much more to say, of course, but at least this is a beginning.