Praxis and Theoria represent the incarnation of the Eastern Christian theology that is negative in itself (apophatic), but not in an absolute sense. Praxis (practice, accomplishment, action) designates the Christian struggle against harmful/evil passions and an endeavor to acquire the necessary virtues. The goal of praxis is apatheia (impassibility, dispassion), which does not necessarily mean insensitive (insensibility) and indifference. Apatheia enables Theoria (sozercanije, reflection, contemplation), which is a mystical contemplation of God in his uncreated Light during the prayerful silence (hesychia, stillness). Theoria reaches its climax in Theosis (deification) of a person that involves the mystical union, so characteristic of eastern Christianity. It needs to be said that besides visible and clear Christian origin, the term praxis stems also from the Stoic philosophy, as the term Theoria stems from the Neo-Platonism philosophy. However, as in the Eastern Christian mysticism, throughout history, they have acquired a fully Christian and orthodox meaning. The process of Christianization of the Praxis and Theoria, started by the Greek church fathers, was completed by St. Gregory Palamas. It is for this very fact that the Praxis and Theoria are essentially determined, a side for a distinctive theology of the Eastern church fathers, by an energism and Palamism. Praxis, Theoria and Theosis as realities are determined by the specific (each one separately) and collective theological context. The specific theological context of Praxis is spiritual cosmology, hamartiology and demonology; of Theoria: hesychasm and theology of the heart; and of Theosis: Palamism - energism and soteriology. The collective theological context of Praxis, Theoria and Theosis is an Eastern Christian theology in the broadest sense of the word. It is important to notice that the Eastern Christian mysticism is in many ways different from other mystical expressions, whether from other religions or Christianity itself. All the above mentioned, including the institutionalization of Eastern Christian mysticism, completely eliminates the possibility that we are dealing with „natural religious” or „universal hyper-religious” mysticism. Praxis, Theoria and Theosis determine the path of Christian perfection in the East. This path is „mystical” only from a western perspective, while for Christians of the East itself, it is regular, „canonical” and the only path of sanctification to man. The Christian perfection in the East is completely differently conceived to the one in the West. Christian, that is, spiritual perfection in the East has never been burdened with moralism or pietistic manifestations, as was the case in the West. In the East, becoming a good and virtuous Christian, by the grace of God, it does not yet mean holiness, neither salvation. Theosis is not a divinization (apotheosis), but a deification. Man does not get divinized, but instead he is deified. God is the initiator and executor of this process, which is why Theosis is phenomenologically deeply determined by divine passive. Theosis finally determines the Eastern Christian view on salvation, which is different from the one in the West. In this sense, for the Christian East, Praxis represents a basis, Theoria a prerequisite (condition) and Theosis a mere content of Christian perfection, holiness, that is, salvation itself. The last chapter of this Thesis, which although at first glance could be seen as an unnecessary addition, was in fact its most important part, because only through comparison of the Eastern Christian mysticism with other mystical paths, was it made possible, within the Hesychast experience of Theosis, to notice the strong and eloquent presence of ontological differentiation and dialectic, the respect for the conceded (donated) otherness, and the highlights of the existential duality in the relationship man - God, even in this kind of the most intimate „mystical union” in Theosis, to which Praxis and Theoria bring. All these things, within mystical paths, which are compared to hesychasm, are or too discreetly and too implicitly present, or dangerously, completely imperceptible.