Up through endless ranks of angels,
Cries of triumph in His ears,
To His heav'nly throne ascending,
Having vanquished all their fears,
Christ looks down upon His faithful,
Leaving them in happy tears.
- LSB 491:1
Forty years the children of Israel wandered in the wilderness before they were led by Joshua across the Jordan into the Promised Land. Forty days after Easter the new, wandering Israel is led by the greater Joshua (Yeshua) across the glassy, crystalline sea to the right hand of God on high. Christ is the beginning of the New Creation; He is the first fruits of those who have fallen asleep (1 Corinthians 15) and the pioneer of our salvation (Hebrews 2:10ff). Today, as C.S. Lewis reminds us, "a new chapter in cosmic history has opened." Christ closed the door to everlasting death by his own death and opened heaven for all as easily as he opened his own tomb. The dragon is slain, the Lamb has conquered and now the King ascends to his throne. All of this (and more as we shall read on below) follows along in joyful refrain as we celebrate the Ascension. For "there is no possibility of isolating the doctrine of the Resurrection from that of the Ascension" (Lewis - Miracles, p. 236). Jesus' resurrection leads to his Ascension. You don't get one without the other. The 'It is Finished' of Good Friday must be extend throughout the whole world. And when one's work is finished they rest, or in Jesus' case, rest by siting down on at the right hand of God.
Christianity simply cannot do without the story of the ascension - just as we cannot do with out the Resurrection. We confess it every Sunday in the creed. According to Lewis, we can only drop the Ascension story (as a real event - for it was seen by more than one person at a time and group hallucination/dreams are impossible) if we are prepared to throw out the Resurrection as well.
We can do so only if we regard the Resurrection appearances as those of a ghost or hallucination. For a phantom can just fade away; but an objective entity must go somewhere - something must happen to it. And if the Risen Body were not objective, then all of us (Christian or not) must invent some explanation for the disappearance of the corpse. And all Christians must explain why God sent or permitted a 'vsion' or a 'ghost' whose behaviour seems almost exclusively directed to convincing the disciples that it was not a vision or a ghost but a really corporeal being. If it were a vision then it was the most systematically deceptive and lying on record [not to mention the most brilliantly, skilled conspiracy ever conceived in history; lying takes work, you know!]. But if it were real, then something happened to it after it ceased to appear. You cannot take away the Ascension without putting something else in its place (Miracles, 243-244).
Now our heav'nly Aaron enters
With His blood within the veil;
Joshua now is come to Canaan,
And the kings before Him quail.
Now He plants the tribes of Israel
In their promised resting place;
Now our great Elijah offers
Double portion of His grace.