The Orthodox pneumatology wholly depends on the credal statements and the Holy Tradition of the undivided Church. The Orthodox theologian makes efforts to acquire the mind of the Holy Fathers, eschewing the polemics. However, the later development in the West leading to Filioque, as well as the problem of the »epiclesis« in Eucharist and the papal claims of infallibility leads if not to the confrontation than at least to a dialogue with the West.
The encounter between God and creature is possible only through the Holy Spirit. In the Orthodox Patristic theology the notion of theleosis is ascribed to the Holy Spirit, Who is among the Three Divine Persons the power of Revalation and completion. The very movement from the Father, through the Son, in the Holy Spirit, reveals the internal life of the Trinity and inspires the entire life of the Church. The movement of the ecclesial life has its beginning in the Holy Spirit and through the Son goes to the Father.
The bifurcation of the Eastern and Western pneumatology started already in the fourth century. St. Augustine of Hyppo beginns his theology with the contemplation on the Essence of God and goes on to the mystery of the Trinity, while the Fathers in the East, for whom the Essence is unknowable and inapproachable, start their theology with the data of Revelation, i.e. the manifestation of the Three Divine Persons, whose unity is seen in the Person of the Father.
For the Orthodox theologian the abiding presence of the Holy Spirit in the Church is the guarantee of the Church's infallibility. Even the »reception« of the Ecumenical Councils' decisions cannot take place without the living testimony of the Holy Spirit in each believer.