It expresses our belief that in Christ human nature, the humanity in which we all share, has entered into the inner life of God in a new and hitherto unheard of way. It means that man has found an everlasting place in God.
Heaven is not a place beyond the stars, but something much greater, something that requires far more audacity to assert: Heaven means that man now has a place in God. The basis for this assertion is the interpenetration of humanity and divinity in the crucified and exalted man Jesus. Christ, the man who is in God and eternally one with God, is at the same time God's abiding openness to all human beings.
Thus Jesus himself is what we call "heaven"; heaven is not a place but a person, the person of him in whom God and man are forever and inseparably one. And we go to heaven and enter into heaven to the extent that we go to Jesus Christ and enter into him. In this sense, "ascension into heaven" can be something that takes place in our everyday lives…
For the disciples, the "ascension" was not what we usually misinterpret it as being: the temporary absence of Christ from the world. It meant rather his new, definitive, and irrevocable presence by participation in God's royal power... God has a place for man!… In God there is a place for us!…"Be consoled, flesh and blood, for in Christ you have taken possession of heaven and of God's kingdom!" (Tertullian).