In the Orthodox Church, salvation is understood primarily as theosis, the infinite process of becoming more and more like God. Theosis may be translated as deification or divinization, and its meaning is that the Christian may become more and more soaked with the divine life, becoming by grace what Christ is by nature. As St. Athanasius the Great (4th century) said, “God became man so that man might become divine.” By participation in the Incarnation, man becomes like Christ. This reality goes far beyond the simple question of going to Heaven after death.
Salvation is a process which encompasses not only the whole earthly life of the Christian, but also the eternal life of the age to come. It is often described in terms of three stages—purification (katharsis), illumination (theoria) and divinization (theosis). Salvation is thus not only becoming sinless (purification), but it is also a progress in being filled with the divine light (illumination). Additionally, it is becoming so filled with God in union with him that the Christian shines forth with the likeness of God, in some cases even literally becoming a bearer of the Uncreated Light, a physically visible light from God that is his presence, such as at the Transfiguration (Matt. 17:1-6; Mark 9:1-8; Luke 9:28-36) or when Moses spoke with God on Mt. Sinai (Ex. 34:29-35). Though the terminology of three stages is sometimes used, there is much overlap between them, and the whole process itself is often termed theosis.
It is only in and through Christ that man can be saved (John 14:6). Salvation cannot be earned, being a free gift from God. Its acquisition, however, requires man’s cooperation with God, because God will not violate the free will of man. A life of repentance and participation in the sacraments is the means by which man cooperates with God, which not only forgives sins through Christ’s atoning sacrifice on the cross but also makes him more like Christ. This cooperation is termed synergeia (synergy), making us co-workers with God (I Cor. 3:9; II Cor. 6:1).
In theosis, man becomes filled with the divine life. He takes on God’s attributes, but he does not become merged with the Holy Trinity. There is union without fusion. Man can become a “god” by grace, not in a polytheistic sense (because there is only one God), but rather in terms of becoming a son or daughter of the Most High by means of adoption (Ps. 82:6; John 10:34). Thus, a classic patristic image of theosis is a sword held in a flame—the sword gradually takes on the properties of the flame (light and heat), but remains a sword. All things are to be gathered together in Christ (Eph. 1:10, 2:6).
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