This is one of any number of "Odd God" stories meant to overturn our notion of how God works and how we are to relate to one another. The younger son in effect tells his father to 'drop dead' or at least recognize that he is so senile, it is time for his sons to take over. The Father does what is most undignified for a semite, 'runs' out to meet his son. This Father, like our heavenly Father forsakes all dignity demonstrates the initiative to embrace us with love. Then all that is asked of us is what is asked of the older brother, that we in turn embrace one another.
I take exception to the persistent suggestion that the younger son has committed the most vile of sins. A consistent reading of the Gospels shows almost scandalously easy forgiveness for those who have committed sins of weakness and momentary lapses. Jesus reserves his strong condemnation for those who misuse power and authority, take advantage of the helpless, scorn those in need, or stand in the way of his mission. This provides a key to understanding the older brother whose sin of self-righteous comes dangerously close to the later category.