“After His resurrection from the dead Jesus appeared to men for a period of forty days after which He “was taken up into heaven, and sat down at the right hand of God” (Mk 16.19; see also Lk 24.50 and Acts 1.9–11).
The ascension of Jesus Christ is the final act of His earthly mission of salvation. The Son of God comes “down from heaven” to do the work which the Father gives Him to do; and having accomplished all things, He returns to the Father bearing for all eternity the wounded and glorified humanity which He has assumed (see e.g. Jn 17).
The doctrinal meaning of the ascension is the glorification of human nature, the reunion of man with God. It is indeed, the very penetration of man into the inexhaustible depths of divinity.
We have seen already that “the heavens” is the symbolical expression in the Bible for the uncreated, immaterial, divine “realm of God” as one saint of the Church has called it. To say that Jesus is “exalted at the right hand of God” as Saint Peter preached in the first Christian sermon (Acts 2.33) means exactly this: that man has been restored to communion with God, to a union which is, according to Orthodox doctrine, far greater and more perfect than that given to man in his original creation (see Eph 1–2).
Man was created with the potential to be a “partaker of the divine nature,” to refer to the Apostle Peter once more (2 Pet 1.4). It is this participation in divinity, called theosis (which literally means deification or divinization) in Orthodox theology, that the ascension of Christ has fulfilled for humanity. The symbolical expression of the “sitting at the right hand” of God means nothing other than this. It does not mean that somewhere in the created universe the physical Jesus is sitting in a material throne.” (Fr. Thomas Hopko, Doctrine and Scripture, Vol. 1, pp. 106-107)