11 And he said: A certain man had two sons:
Augustine: Two sons is understood to be God having two nations, as if they were two roots of the human race; and the one composed of those who have remained in the worship of God, the other, of those who have ever deserted God to worship idols.
Cyril: Some say that by the elder son is signified Israel according to the flesh, but by the other who left his father, the multitude of the Gentiles.
12 And the younger of them said to his father: Father, give me the portion of substance that falleth to me. And he divided unto them his substance.
Ambrose: The Divine patrimony is given to them that seek; nor think it wrong in the father that he gave it to the younger.
13 And not many days after, the younger son, gathering all together, went abroad into a far country: and there wasted his substance, living riotously.
Chrysostom: The younger son set out into a distant country, not locally departing from God, who is every where present, but in heart.
Ambrose: What is more afar off than to depart from one’s self, to be separate not by country but by habits. For he who severs himself from Christ is an exile from his country, and a citizen of this world.
Titus of Bostra: Hence too was the prodigal denominated one who wasted his substance, that is, his right understanding, the teaching of chastity, the knowledge of the truth, the recollections of his father, the sense of creation.
Augustine: He calls a riotous or prodigal life one that loves to spend and lavish itself with outward show, while exhausting itself within.
Whoever wishes to be so like to God as to ascribe his strength to Him, let him not depart from Him, but rather cleave to Him that he may preserve the likeness and image in which he was made. But if he perversely wishes to imitate God, that as God has no one by whom He is governed, so should he desire to exercise his own power as to live under no rules, what remains for him but that having lost all heat he should grow cold and senseless, and, departing from truth, vanish away.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. III (London: Rivington, 1843).