You talk about the Kingdom of God continually. What is this Kingdom of God?
The Kingdom of God is what Christ has brought to the world. The Gospel is full of Christ’s insistence that the Kingdom of God is given to men by His coming. It is a Kingdom not of this world, but of God, a Kingdom of everlasting life in union with God, the Trinity.
Thus, we define the Kingdom of God as life in and with God. The Orthodox believe that this life is communicated to men in the Church through Christ and the Holy Spirit. It is a life where men worship and obey God and do His will by the presence and power of His Spirit.
One saint has even defined the Kingdom of God as life in the Holy Spirit, which is the same definition given by Orthodox to the Christian Church itself.
What we know in the Church, in the Holy Spirit, of communion with God the Father through Jesus Christ, remains still a mystery. The Kingdom is really here, but in symbol and sacrament. At the end of the ages this Kingdom will come with observation, with power and glory, when Christ will be revealed and God will be “all in all.”
Thus because we Orthodox believe that the Kingdom is already given to those who believe, and that the righteous dead have even a greater access to this Kingdom than we have on earth because of our mixture with the evil of this age, we insist that “heaven” is not a locatable place within the space of our created universe, but a spiritual, divine, condition of existence which will fill the universe at the end of time. It is “eternal life” already revealed to the saints in death and to the holy people of God within the sacramental life of the Christian Church.