The Ascension of Christ is his final physical departure from this world after The Resurrection. It is the formal completion of his mission in this world as the Messianic Saviour.
It is his glorious return to the Father after having accomplished the work the Father had sent him to do (John. 17: 4-5)
What was his work?
To sanctify mankind and to unite him with God. Ascension of Jesus Christ is the final act of this work.
The Son of God came "down from heaven" and now having accomplished all things, he returns to the Father bearing for all eternity the wounded and glorified humanity which he had assumed.
(John. 17)
The doctrinal meaning of Ascension is the glorification of human nature, the reunion of man with God.
It's the very penetration of man into the inexhaustible depths of divinity. This is what it means when it is said that he sat on the right hand of God. Man has been restored to communion with God, to a union which is far greater and more perfect than that given to man in his original creation.
Man was created with the potential to be a "partaker of the divine nature". This participation in divinity is what we Orthodox call Theosis or Deification and this is what is