“The Ascension is a festival of the future of the world. The flesh is redeemed and glorified, for The Lord has risen for ever. We Christians are, therefore, the most sublime of materialists.” Karl Rahner 
Ascension Day is not meant to be a window into the oddities of first century cosmology. We all know we don’t live in a three-tiered universe. Our affirmation of the Ascension as a matter of faith does not require some tortured obsession with reconciling the apparent difficulties that rise from divine accommodations that made the Incarnation intelligible in its original cultural context. On the other hand, I remember hearing John Shelby Spong openly deride the idea of “Spaceman Jesus” some years ago. As then, I still think these are all parts of the one massive exercise in missing the point that we call by the name “modernity”.
Ascension is a profound demonstration of the deep eschatological claims and anthropological implications of the Christian witness to the resurrection. The Ascension of Jesus closes down the incipient gnosticism of otherworldly and escapist notions of Christian faith even as it deploys images of departure and supernatural power. It does this by describing the taking up the corporeal reality, the body, of the Son into the Godhead. In so doing, Ascension certifies our confidence in the salvation that comes through God’s generative acts of Incarnation and Resurrection.
And while the Ascension points to these weighty theological concerns, the significance of this day is by no means an esoteric intellectual exercise rising from some fragment of equally esoteric biblical literature. For the full flowering of salvation proclaimed in the Ascension is to be embodied in the life of the Church as a continuing act of proclamation: The absence of Jesus makes room for the possibility of his presence through his people. So the liturgical and devotional function of Ascension day is not primarily about the enthronement of Jesus as Lord, but should be regarded for its capacity to hold forth a vision of the role of the Church in the world as the “Body of Christ” which still remains on earth. This vision is distilled in the tangible signs of Eucharist as the central formative act of our worship: the Bread that is the Body of Christ sustains the Body of Christ that is the Church who bears witness to the ascended Christ as healing Lord—the one who affirms and redeems our embodied existence. Furthermore, God’s embrace and reception of our materiality via the person of Christ becomes the pattern of our total acceptance and affirmation of the self-organizing complexity of the material realm in all its forms and expressions.
What this all means is the truth of Ascension is to be lived out in an earthed spirituality that joyfully embraces the deep pleasures and wonder of our lives and world, that grieves and seeks to heal and mend where disruption and despair are known, that affirms “the natural world of sea, rock and earth as being redolent with divine glory, and recognizes Christ in the faces of friends and strangers.” 
The Ascension of Jesus articulates a kind of manifesto that calls us not to rise to heavenly places of prestige, privilege and power, but to run unhindered into the embodied fullness of the human experience—to joyfully proclaim in our living that one day here on this good earth made new, in our bodies, humanity will dwell fully and freely with God precisely because God has already received us in the body of Christ.
The Trinity has purposed to make God’s eternal dwelling place here with us on earth: In our eating and loving, our play and work, our laughter and our limitations. Even now the Father and Spirit commune with the risen and ascended Incarnate Son, and their communion is more sensible than we can ever conceive. That unfettered communion is our hope and carries in it the final answer to all the deepest longings of that material complex we call the human being. And lest we forget, that communion is also the reordering hope of all creation. This is the Gospel.
In the incarnated union of God and Humanity—that is, in the person of Jesus, The Christ—we discover the end and purpose of all things—that is, full communion between the Trinity and a restored humanity and creation. In the ascended Son we see the means by which the Trinity will bring their desires to fruition. The Ascension is the inauguration of this consummating delight. It marks the return and reception of the human race to our Source. And it is the harbinger of our reception of the Spirit that frees The Body to be the vanguard of a humanity and creation repaired and made new.
—  Karl Rahner, “The Festival of the Future of the World”, Theological Investigations, vol. 7, 180  Christopher Irvine, Celebrating the Easter Mystery, 112