Jesus was an apocalyptic. He saw the coming of a new world brought by God to earth through the son of man (who may or may not have been him). His parables are told in the setting of this apocalyptic vision for the near future ("There are those who are here today who will not taste death before these things will come to pass"). In that context, the son who stayed on the farm was really the victim of his own earthly expectations. The new world order that God will bring when he sends the son of man to rule the earth will not be that of human concerns, but of those of God's love. A God of love will love his sons equally, however prodigal one might be, and in fact rejoices whenever one returns, as any father would. It's not about the fortune, it's about love of his son. The son who stays has that love all the while as well, he just sees the fortune as its manifestation, instead of the love itself as his priviledge. His expectations were earthly, but God's love is not.
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