I really am enjoying reading The Experience of God: Orthodox Dogmatic Theology, vol. 1 by Dumitru Stăniloae. Here is a description of deification or theosis which I found particularly impressive, given in the context of the role of church dogma as a retelling of the plan and means of the salvation/deification of man through God in Jesus Christ:
We have seen above that there is no salvation for the human person apart from communication with the supreme Person. Apart from this communication, the power to strengthen oneself spiritually is nowhere to be found, nor the power to remain eternally as persons without being reduced to the level of nature, or virtually to that level.
The dogmas of the Christian faith specify, moreover, that the salvation of man is assured as an eternal, happy existence only if his relation with the supreme Personal reality is so close that the powers and attributes of God will be stamped indelibly upon him through what is called deification. For this deification makes man, together with God, a bearer of divine attributes and powers that completely overcome that tendency which the human body has towards corruption (p. 65).
In other words, humanity can only be saved if it exists in a sort of communion with God, who is the supremely Personal reality in the Holy Trinity. And this salvation consists in a sort of communication of attributes between God and the human person, by which the human person is made capable of living rather than dying, of being fulfilled and realized rather than corrupted. For Stăniloae, this is something accomplished through the incarnation, by virtue of which humanity in the person of Christ himself has been transformed and fulfilled and perfected; then, humanity receives the free invitation to unite itself to Christ, through his example in the word as well as through union with him in his real presence in the Eucharist.
This latter element is critical, however: there must be a free approach of Christ, not a compelled one.
Thus, the dogmas are necessary for salvation because they express Christ in his saving work. But Christ saves us only if we open ourselves to him, if we believe in him. Thus, the Christian dogmas express the powers of Christ in his saving action, provided only that we believe what they express (ibid.).
Apart from an openness to Christ as Christian dogma presents him, they can have no salutary effect on the life of an individual person. This is an obvious enough point, and accords with what Christ himself says in the gospels: unless you believe in him, unless you accept him and trust him, he cannot save you and perform any good work for you. Everything will be ineffective, you will second-guess and doubt everything, and you cannot be saved that way.