Most of the canvas is taken up by the apostles, who are being drawn up with Christ with their eyes, as the two feet move off the top of the painting, presumably into the spiritual realms.
One of the blessings of the modern age to most readers is the ability to immediately research a passage via the Internet. In this case I was able to find the painting very quickly and easily. But I saw it in a completely different way. Rohr draws our attention to Jesus' feet. Recall an image of Jesus' crucifixion. Notice the feet. They are pointed down; nothing supports them. Gravity is the instrument of death, as the full weight of the body squeezes out of the breath (spirit) of Jesus. Back to the feet. In Kulmbach's painting, the feet are not pointed down; they are in a position as if Jesus is preparing to land on earth. Is this painting of Jesus' Ascension or his Second (Final?) Coming. Notice also the disciples. They are old men. I think most Christians imagine them to be much younger.