Spong illuminates probable early Christian psychology. (1) Peter experienced an intolerable contradiction between Jesus' entirely God-centred, God-affirming life and his God-cursed death by execution. This was the theological Problem of Evil and the theme of the Book of Job writ large. Peter must have experienced intensely the problem which Christian theology sometimes poses very abstractly as a contradiction between omnipotence and infinite goodness on the one hand and suffering on the other hand. Peter's solution was, first, to re-interpret the death as expressing the life, as somehow an ultimate expression of unconditional love, and, secondly, as far as possible, to deny the death by affirming a Resurrection that at that stage was spiritual, not physical, and believed to have occurred in Galilee, not in Jerusalem. Jesus was risen in God, not, as described later, walking around in Jerusalem. That makes sense of the texts and of Peter's probable psychological processes.
However, Spong interprets all the accounts of Jesus' ministry as neither history nor biography but "midrash", meaning scripturally-based stories written to proclaim a Messiahship that had not yet been claimed or recognised while Jesus was still alive. Thus, all we know about Jesus is that he made a big impression on Peter and on some others. For Spong, this is enough for us now to proclaim Jesus' Messiahship and spiritual Resurrection. For me, it is not. I do not worship the Hebrew deity and find spiritual meaning in another tradition. Jews, Muslims and Sikhs worship the One God but do not identify Jesus with him. A Spongian creed would contain the unconvincing affirmation: "I believe that it would be fair to say that in that moment Peter felt himself to be resurrected."
(1) Spong, John Shelby, Resurrection: Myth or Reality? New York, 1994.