Forty Days after the Resurrection of Jesus Christ, the Acts of the Apostles records Jesus' ascension into heaven (Acts 1:2). The ascension celebrates the reality of the God-Man Jesus Christ's returning to the Father. The Ascension is the final component of the paschal mystery, which consists also of Jesus' Passion, Crucifixion, Death, Burial, Descent Among the Dead, and Resurrection.
The Catholic Catechism summarizes three important theological aspects (with which most Christian churches agree) of the Ascension concisely:
Christ's Ascension marks the definitive entrance of Jesus' humanity into God's heavenly domain, whence he will come again (cf. Acts 1:11); this humanity in the meantime hides him from the eyes of men (cf. Col 3:3).
Jesus Christ, the head of the Church, precedes us into the Father's glorious kingdom so that we, the members of his Body, may live in the hope of one day being with him for ever
Jesus Christ, having entered the sanctuary of heaven once and for all, intercedes constantly for us as the mediator who assures us of the permanent outpouring of the Holy Spirit (665-667).
The reality of Christ's Ascension is so important that the creeds (the basic statements of belief) of Christianity all affirm, in the words of the Apostles' Creed, that "He ascended into heaven, sits at the right hand of God the Father almighty; from thence He shall come to judge the living and the dead."
Christ's bodily Ascension foreshadows our own entrance into Heaven not simply as souls, after our death, but as glorified bodies, after the resurrection of the dead at the Final Judgment. In redeeming mankind, Christ not only offered salvation to our souls but began the restoration of the material world itself to the glory that God intended before Adam's fall.