This thy son - This son of "thine." This is an expression of great contempt. He did not call him "his brother," but "his father's son," to show at once his contempt for his younger brother, and for his father for having received him as he did. Never was there a more striking instance of petty malice, or more unjustifiable disregard of a father's conduct and will.
Thy living - Thy property. This is still designed to irritate the father, and set him against his younger son. It was true that the younger son had been guilty, and foolish, and ungrateful; but he was penitent, and "that" was of more consequence to the father than all his property; and in the joy that he was penitent and was safe, he forgot his ingratitude and folly. So should the older son have done.

This thy son - This son of Thine - words expressive of supreme contempt: This son - he would not condescend to call him by his name, or to acknowledge him for his brother; and at the same time, bitterly reproaches his amiable father for his affectionate tenderness, and readiness to receive his once undutiful, but now penitent, child!
For Him - I have marked those words in small capitals which should be strongly accented in the pronunciation: this last word shows how supremely he despised his poor unfortunate brother.

But as soon as this thy son was come,.... He will not own him in the relation of a brother, though the father had owned him in that of a son; and the offence he took was, that the fatted calf should be killed, or that a crucified Christ should be preached; that he should be preached at all, and much less that he should be preached to sinners; and still less that he should be preached so soon to them, as soon as ever they became sensible of their sin, as it was the will of his father it should be: for such are not to be sent away to cleanse themselves from sin by any thing they do, and then apply to Christ; or to heal themselves, and then come to him for a cure; or to get peace by doing so, and then come to him for rest; or to do any thing to fit themselves for him, for their case requires present help: now at this the self-righteous man is displeased. The elder brother would have had another method taken with this younger son: he would have had him soundly whipped with the rod of the law, for his former sins; and sent into the fields along with him to work out his salvation; and not to have a rag put upon him, or a shoe on his foot, or a morsel of bread given him, till he had earned them; but instead of this, to be received and entertained in the manner he was, and so soon, highly provoked him: for he thought such a conduct was unbecoming God, and his moral perfections; and what his brother was undeserving of; and opened a door to, licentiousness; and highly reflected on his services, as of no value and regard.
Which hath devoured thy living: given to his son; that part of his goods he had divided to him, Luke 15:12
with harlots; in rioting and drunkenness, in chambering and wantonness, in gluttony and debauchery:
thou hast killed for him the fatted calf; See Gill on Luke 15:23