Forty days after the Resurrection, Christ leads His disciples out to the Mount of Olives, blesses them, and is taken up into heaven. The Ascension is not a departure that leaves us orphaned; it is the raising of human nature itself to the right hand of the Father. Where the Head has gone, the body may follow, our flesh, taken by God at the Nativity, is now enthroned in glory.
The feast answers a fear as old as humanity: that heaven is closed to us. In Christ ascended, it is opened; a man sits on the throne of God, and our nature is no longer a stranger there. The disciples return, the Gospel says, not in grief but with great joy, for the Lord who ascended has promised to send the Comforter and to be with them always.
The Ascension is measured from Pascha and always falls on a Thursday, ten days before Pentecost. It completes the Lord's earthly work and opens the short expectant season before the coming of the Spirit.