For Peter—as, indeed, for the whole Church—the transfiguration of Jesus on Mount Tabor became a testimony to His majesty. What happened there? The apostles undoubtedly saw their Teacher on Tabor in a transfigured body, a body that by its nature belongs to the Kingdom, the same kind of body in which they would later see Him risen. But what was the meaning of the vision? And what had preceded it in the Yahwist and Jewish traditions?
This was, quite clearly, a revelation of the Kingdom. Such revelations had been known since ancient times. Visions of the Throne of Glory had become part of the liturgical tradition as early as Solomon's era, and they were nothing other than revelations of the Kingdom. The Kingdom had not yet “drawn near,” of course, but its glimmers would nevertheless sometimes penetrate the untransfigured world. At times it was partly revealed in other ways as well, particularly in visions of Yahweh's heavenly chariot, such as the one Ezekiel saw. That chariot bore the same Throne of Glory that others—Isaiah of Jerusalem, for example—saw in the Temple.
Now the vision of the transfigured Saviour took the place of the vision of the Throne of Glory. This too, of course, was a revelation of the Kingdom, and the apostles understood it perfectly. They failed to understand only one thing: for the Kingdom to enter the world definitively, the Messiah had to follow His path to the end, and that end would be not victory in a messianic war but death on the cross followed by resurrection. Yet the fact that Jesus appeared before the apostles in this way became convincing testimony for them that He was the Messiah. The Kingdom belongs to the Messiah, and if their Teacher now appeared before them as King—as was evident—then He truly was the Messiah, and the Kingdom truly belonged to Him. It is no accident that, precisely after the vision on Tabor, Jesus Himself began to speak especially often and at length with the apostles about His death and resurrection. They now knew almost everything; what remained was for them to grasp the essential point: exactly how the Kingdom would enter the world.
Yet the essential point proved to be the hardest, above all because it contradicted every accepted notion of the Messiah and the Kingdom at that time. The misunderstandings faded after Pentecost, but the memory of this remarkable event remained—and was preserved by the Church.
