SOURCE: Orthodoxworld.ru
The Lord ascended to Heaven not to sadden us with His departure, but in order to do what was best for us. It is to your advantage that I go away. He had told His disciples. [For] if I do not go away, the Comforter will not come to you (John 16:7). I will pray the Father, and He will give you another Comforter, to be with you for ever, even the Spirit of truth.... The Comforter, the Holy Spirit, Whom the Father will send in My name. He will teach you all things (John 14:16, 26). The Savior saw that His mission on earth was accomplished. The goal of His Incarnation was to proclaim the Divine Truth to the world, to direct men onto the path of repentance and salvation, and deliver us from Eternal Death. The Lord accomplished our salvation and man acquires it through the action of the Holy Spirit.
The Lord knew the trials and tribulations that would be endured by His disciples - mockings, scourgings, imprisonment and even death. And thus the Lord ascended to His Heavenly Father that the Spirit might descend from the Father as the Comforter, and fortify His Friends.
The Lord ascended to Heaven in order to prepare for us, too, the path to the Heavenly Mansions, to open the Gates of Paradise, and Himself to be our Guide. Heaven that had been closed to men before the Resurrection now at the Ascension was opened by Christ the Savior.
The Ascension of Our Lord Jesus Christ. Greece. XVI century
The Lord ascended to intercede for us with His Heavenly Father. Towards the end of His earthly mission He had said: I go to prepare a place for you. And when I go and prepare a place for you, I will come again and will take you to Myself, that where I am you may be also (John 14:2-3). This same thought was also expressed by the great Preacher of Christ's teaching, St. Paul, in the Epistle to the Hebrews: Christ has entered, not into a sanctuary made with hands, a copy of the true one, but into heaven itself, now to appear in the presence of Cod on our behalf (Heb. 9:24). These words fill us with hope, for we now have in Heaven a great Mediator and Advocate for the world with God - Christ Our Lord.
Our Lord ascended in a cloud on high, symbolizing the rising smoke of an acceptable sacrifice. Thus the sacrifice was accepted by God and Christ the Lamb that was slain is ushered into the preserve of God where He will be eternally offered in the Holy Eucharist. Therefore we must be worthy of the great mercies of God, capable and ready to receive them. All the power, all the fruit of His divine Ascension, therefore, belong to us, for when He ascended on High, He led captivity captive, and gave gifts to men (Eph. 4:8). This is why the Church repeatedly proclaims: "Clap your hands, all you nations, for Christ is ascended up to the place where He was before" [from the Vespers of the Feast].
Troparion of the Feast (Tone 4)
O Christ God, Thou hast ascended in Glory, granting joy to Thy disciples by the promise of the Holy Spirit. Through the blessing they were assured that Thou art the son of God, the Redeemer of the world!
Kontakion of the Feast (Tone 6)
When Thou didst fulfill the dispensation for our sake, and unite earth to heaven: Thou didst ascend in glory, O Christ our God, not being parted from those who love Thee, but remaining with them and crying: I am with you and no one will be against you!