Why was the prodigal son spoken harshly of by his elder brother? In the parable of the Prodigal Son, Jesus narrates : "Not long after that, the younger son got together all he had, set off for a distant country and there squandered his wealth in wild living" (Lk 15:13) 

But,  when the prodigal son returns home to a warm welcome, his elder brother comments to his father :".. when this son of yours who has squandered your property with prostitutes comes home, you kill the fattened calf for him!".

One is amused by the remarks of the elder son with reference to the off-home stay of his younger brother, which in fact, was not the narrative given by the story-teller (Jesus). My question is: was Jesus intending to bring out the degeneration of relations over property and wealth  by 'making' the elder son speak harshly of the younger one ? Are there some commentaries available on this subject ?
The brother's harsh remark betrayed that he had the spirit of a hireling, rather than that of a son. His service for the father was not one motivated by love, but rather by the promise of reward. Even though he had not gone into great excesses like the younger brother, his failure to show the same concern for his lost brother as the father did showed that he had yet to discern the love of the father for himself. "He that loveth not knoweth not God, for God is love" (1 John 4:8). 

Ellen White in her commentaries in the book Christ's Object Lessons goes into great detail. 


  By the elder son were represented the unrepenting Jews of Christ’s day, and also the Pharisees in every age, who look with contempt upon those whom they regard as publicans and sinners. Because they themselves have not gone to great excesses in vice, they are filled with self-righteousness. Christ met these cavilers on their own ground. Like the elder son in the parable, they had enjoyed special privileges from God. They claimed to be sons in God’s house, but they had the spirit of the hireling. They were working, not from love, but from hope of reward. In their eyes, God was an exacting taskmaster. They saw Christ inviting publicans and sinners to receive freely the gift of His grace—the gift which the rabbis hoped to secure only by toil and penance—and they were offended. The prodigal’s return, which filled the Father’s heart with joy, only stirred them to jealousy. 
  In the parable the father’s remonstrance with the elder son was Heaven’s tender appeal to the Pharisees. “All that I have is thine”—not as wages, but as a gift. Like the prodigal, you can receive it only as the unmerited bestowal of the Father’s love. 


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  It is true that you claim to be a child of God; but if this claim be true, it is “thy brother” that was “dead, and is alive again; and was lost, and is found.” He is bound to you by the closest ties; for God recognizes him as a son. Deny your relationship to him, and you show that you are but a hireling in the household, not a child in the family of God. 
  Though you will not join in the greeting to the lost, the joy will go on, the restored one will have his place by the Father’s side and in the Father’s work. He that is forgiven much, the same loves much. But you will be in the darkness without. For “he that loveth not knoweth not God; for God is love.” 1 John 4:8.