Luke 15:13

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.

For it follows, And not many days after, the younger son gathered all together, and took his journey into a far country. For 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. Fitly then does he waste his patrimony who departs from the Church. Now there came to pass in that country a famine not of food but of good works and virtues, which is the more wretched fast. For he who departs from the word of God is hungry, because man does not live on bread alone, but on every word of God. (Matt. 4:4.) And he who departs from his treasures is in want.

(ut sup.) The younger son set out into a distant country, not locally departing from God, who is every where present, but in heart. For the sinner flees from God that he may stand afar off.

(de Quæst. Ev. lib. ii. qu. 33.) But that which is said to have taken place not many days after, namely, that gathering all together he set out abroad into a far country, which is forgetfulness of God, signifies that not long after the institution of the human race, the soul of man chose of its free will to take with it a certain power of its nature, and to desert Him by whom it was created, trusting in its own strength, which it wastes the more rapidly as it has abandoned Him who gave it. Hence it follows, And there wasted his substance in riotous living. But he calls a riotous or prodigal life one that loves to spend and lavish itself with outward show, while exhausting itself within, since every one follows those things which pass on to something else, and forsakes Him who is closest to himself.

(Esai. 3, 23.) Besides, it belongs more to the character of the aged to have an old man's mind and gravity, than his hoar hairs, nor is he blamed who is young in age, but it is the young in habits who lives according to his passions.