Everything the father had, had been distributed, yet the older son who benefited all was begrudging the love the father showed to his prodigal brother and refused to participate in the joy of his younger brother's return, he complained he was never rewarded for faithful service and obedience. He had never been given a fatted calf with a great feast. With restoration of a lost soul there is joy but with one who is obstinate, ungrateful and unreconciled there was no cause for celebration. The older son, thinking himself far more worthy, was described by Jesus for the benefit of The Jewish Religious leaders. They and the older son did not understand the father's actions, which showed these men who were to lead the nation spiritually did not really understand God at all.
Repentant sinners are to be accepted wholeheartedly.
Likened to the Pharisees and Scribes who had access to all the riches of God's Truth, the elder son never really possessed any of the treasure enjoyed by a repentant sinner. The older brother should have rejoiced and celebrated with the others, because he did not, it showed his state of heart. The point is repentance is needed before forgiveness, the young man left demanding but came back begging and humbly asking. The younger son will always be a description of those in disgrace, just as the older brother is a pattern of right priorities. The elder brother had the same unforgiving attitude of the Pharisees, Saducees, Scribes, Elders, Levites towards sinners even though they had repented.