The Kingdom of God
God’s gift of eternal life in Christ and the Holy Spirit is the Kingdom of God. Jesus has brought the Kingdom of God to the world through the Spirit in the Church. Spiritual life is life—already now—in the Kingdom of God.
Fear not, little flock, for it is your Father’s good pleasure to give you the kingdom. Sell your possessions and give alms; provide yourselves with purses that do not grow old, with a treasure in the heavens that does not fail, where no thief approaches and no moth destroys. For where your treasure is there will your heart be also(Lk 12:32-34).
To live already now in the Kingdom of God is to live in freedom from sin and death in the gracious life of Christ and the Church. A person who has died to sin with Christ in baptism and has been sealed with the gift of the Holy Spirit in chrismation and who participates in Christ’s Body and Blood in the eucharist is already a member of the Kingdom of God.
… for through Christ we have access in one Spirit to the Father. So then you are no longer strangers and sojourners, but are fellow citizens with the saints and members of the household of God, built upon the foundation of the apostles and prophets. Christ Jesus Himself being the cornerstone, in whom the whole structure is joined together and grows into a holy temple in the Lord, in whom you also are built into it for a dwelling place of God in the Spirit (Eph 2:18-22).
The Church is called the Kingdom of God on earth; and the presence and power of the Kingdom is identified with the indwelling of the Holy Spirit who abides in the faithful bringing to them the presence and power of God the Father through His Son Jesus Christ.
Thus the Apostle Paul has said, “The Kingdom of God is… righteousness and peace and joy in the Holy Spirit; he who thus serves Christ is acceptable to God and approved by men” (Rom 14:17-18). And Saint Gregory of Nyssa (4th c.) citing the earlier tradition of Christians said simply: “The Kingdom of God is the Holy Spirit. …The Kingdom of the Father and the Unction of the Son.” It has always been understood in the spiritual tradition of the Orthodox Church that to the measure with which one is filled with the Spirit of God, to that same measure he is united with Christ and is in communion with the Father, becoming His child and a member of His Kingdom. Thus it is the teaching that the “acquisition of the Holy Spirit” in “seeking first the Kingdom of God and His righteousness” (Mt 6:33) is the sole purpose and content of man’s spiritual life. It is for this, and this alone, that man has been created by God.
…Walk by the Spirit, and do not gratify the desires of the flesh. For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh; for these are opposed to each other. …Now the works of the flesh are plain: immorality, impurity, licentiousness, idolatry, sorcery, enmity, strife, jealousy, anger, selfishness, dissension, party spirit, envy, murder, drunkenness, carousing, and the like. …those who do such things shall not inherit the Kingdom of God(Gal 5:16-21).
From:The Orthodox Faith by Fr. Thomas Hopko