Through His life in the flesh on earth, the God-Man founded His theanthropic Body, the Church, and in this way prepared the earthly world for the Holy Spirit’s coming into the world, and His life and activity in the Body of the Church as the Soul of that Body.
On the holy Day of Pentecost, the Holy Spirit descended from heaven into the theanthropic Body of the Church and remains eternally in it as its life-giving Soul (Acts 2:1-47).
This visible theanthropic Body of the Church was constituted by the holy apostles with their holy faith in the Theanthropos, the Lord Jesus, as the Savior of the world, as perfect God and perfect Man.
The descent and activity of the Holy Spirit in the theanthropic Body of the Church is because of, and for the sake of, the Theanthropos (cf. Jn 16:7-13; 15:26; 14:26). “For His sake the Holy Spirit entered into the world.”
[…] All His [the Spirit’s] activity is of one essence with the theanthropic ascesis of the salvation of the world by the Lord Christ.
Pentecost is, with all the immortal gifts of the Triune Godhead, of the Holy Spirit Himself, intended for the holy apostles; the holy apostolic Faith and Tradition, the hierarchy and everything that is apostolic and theanthropic.
The Day of the Holy Spirit, which began on the Day of Pentecost, is ever present in the Church in the inexpressible fullness of all the divine gifts and the life-giving powers (Acts 10:44-48; 11:15-16; 15:8-9; 19:6).
Everything in the Church comes about through the Holy Spirit, from the least to the greatest. When the priest blesses the censer before censing, he prays to the Lord Christ to “send down the grace of the Holy Spirit.”
The clearest testimony that the entire life of the Church comes from the Holy Spirit is at the consecration of a bishop, when God’s indescribable miracle, holy Pentecost, is repeated and the fullness of grace is given.
There is no doubt that the Lord Christ is in the Church through the Holy Spirit, and that the Church is in the Lord Christ through the Holy Spirit. The Lord Christ is the Head and Body of the Church; the Holy Spirit is its Soul (cf. I Cor. 12:1-28).
From the very beginning of the theanthropic dispensation of salvation, the Holy Spirit has made Himself a part of the foundation of the Church, the foundation of the Body of Christ, by “bringing about the incarnation of the Logos in the Virgin.”
In fact, every holy mystery and holy virtue is a little Pentecost; in them, the Holy Spirit descends upon us, into us. He descends in His essence, He, “the richness of the Godhead,” “the grace of the open seas,” “from Him come grace and life for every creature.”
Justin Popovich (1894-1979; Orthodox Church): from The Orthodox Church and Ecumenism @ Ora at Labora.