The term theosis is from the earliest (2nd century) Church fathers and refers to the Christian goal and purpose of life. The word theosis became popular in Greek writings from the 2nd century onward but echoes the concept expressed in the word yoga in this sense because yoga, from the Sanskit, means to be yoked to God, to have the divine energies as one's yoke-fellow. The fundamental vocation and goal of each and every person is to share in the energies of God. The descent of the energies of God in the person of Yesu Christ has made possible the human ascent to God through the work of the Holy Spirit our Father and Holy Wisdom our Mother. Eastern Christianity believes that each devotee is involved in a movement toward God which is known as theosis or deification.
Theosis describes the spiritual pilgrimage in which each person becomes ever more perfect, ever more holy, ever more united with God. It is not a static relationship, nor does it take place only after death. On the contrary, theosis is a movement of love toward God which all spirit beings are involved in. For the devotee it begins even before the the rites of Initiation and it continues throughout this life, as well as the life which is to come.
Salvation means liberation from the impulse to sin, thus liberation from evil and resulted incarnation into the human body which is subjected to death, disease and the wiles of the flesh. Redemption means our repossession by God. In Eastern Christianity, both salvation and redemption are within the context of theosis. This rich vision of Christian life was expressed well by Saint Peter when he wrote in the early pages of his second Epistle that we are called "to become partakers of the Divine nature." It was also affirmed by Saint Basil the Great when he described humanity as the creatures who have received the order to become gods. And as the 2nd and 3rd Sayings of Yesu goes;
(2)"Yesu said, ‘Let one who seeks not stop seeking, until one finds. When one finds, one will be disturbed. When one is disturbed, one will be amazed, and will reign over all.'
(3) "Yesu said, If your leaders say to you, ‘Behold, the kingdom is in the sky,' then the birds in the sky will get there before you. If they say to you, ‘It is in the sea,' then the fish will get there before you. ‘Rather, the Kingdom is inside you and outside you. When you know yourselves, then you will be known, and understand that you are children of the Living God. But if you do not know yourselves, then you live in poverty and embody poverty."
Church of the East inherited from Yesu our Lord (our Example, our Template and Teacher), an understanding of theosis as a union with the energies of God and not with the essence of God which always remains hidden and unknown. However, the experience of the Church testifies that this is a true union with God. It is also one which is not pantheistic, because in this union the divine and the human retain their unique characteristics. Thus, in this sense, Church of the East proclaims Yesu's message that human life reaches its fulfillment only when it becomes divine - as Yesu's prayer in St. John's Gospel chapter 17 goes, "I pray not only for these but also for those who through their (the apostles') teaching will come to believe in me. May they all be one, just as, Father, you are in me and I am in you, so that they also may be in us, ..."
Theosis is a process not an event. Theosis is the process of becoming in Christ. Theosis is the process of becoming authentic human beings. Theosis is thus the Way, the walk, the purpose of life.