The celebration of the Ascension is a celebration of the culmination of our Lord’s redeeming work here on earth, and it is the final glorification of Christ in His humanity before the Second Coming.
Consider what we celebrate: not simply the Son of God ascending to heaven - because as God, He never was absent from heaven - but the first entrance of our human nature, our human flesh into heaven. Before Christ died, rose from the dead, and ascended into heaven, human nature could not enter into Paradise. Now we have a concrete hope and sign of our own ascension into glory - body, and soul - on the Last Day! What an amazing event! Christ and His Blessed Mother are now present
bodily in eternal glory.
The Apostles were left looking heavenward - and that is indeed where our hearts should reside. In the Mass, the priest exhorts you to “lift up your hearts!” This is how the Christian should always live, with hope. Of course, the Apostles were then told to carry on with their mission of evangelizing the world, not staring with mouths agape at the sky. We too must fulfill our daily obligations, the demands of our vocations, and the daily tasks which burden us here below, but even though we are not literally looking heavenward, we should always be living in hope of that day where we will behold Christ in His glorified humanity.