The following sermon was written as a letter from St. Gaudentius in reply to a request made to him by Serminium, regarding the proper understanding of Luke 16:1-13.
First, here's what Luke's Gospel states:
1 He also said to the disciples, "There was a rich man who had a steward, and charges were brought to him that this man was wasting his goods. 2 And he called him and said to him, 'What is this that I hear about you? Turn in the account of your stewardship, for you can no longer be steward.' 3 And the steward said to himself, 'What shall I do, since my master is taking the stewardship away from me? I am not strong enough to dig, and I am ashamed to beg. 4 I have decided what to do, so that people may receive me into their houses when I am put out of the stewardship.' 5 So, summoning his master's debtors one by one, he said to the first, 'How much do you owe my master?' 6 He said, 'A hundred measures of oil.' And he said to him, 'Take your bill, and sit down quickly and write fifty.' 7 Then he said to another, 'And how much do you owe?' He said, 'A hundred measures of wheat.' He said to him, 'Take your bill, and write eighty.' 8 The master commended the dishonest steward for his shrewdness; for the sons of this world are more shrewd in dealing with their own generation than the sons of light. 9 And I tell you, make friends for yourselves by means of unrighteous mammon, so that when it fails they may receive you into the eternal habitations. 10 "He who is faithful in a very little is faithful also in much; and he who is dishonest in a very little is dishonest also in much. 11 If then you have not been faithful in the unrighteous mammon, who will entrust to you the true riches? 12 And if you have not been faithful in that which is another's, who will give you that which is your own? 13 No servant can serve two masters; for either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve God and mammon."
The Unjust Steward 
By St. Gaudentius, Bishop of Brescia (d. AD 410)
Patroligia Latina, J.P. Migne, ed. (Paris, 1841-1855), 20, col. 971, Sermo 18
… I come now to what you so earnestly asked of me; and what I believe in this matter I shall tell you as briefly as I can; and without criticism of how any one else may interpret it, provided his explanation does not lessen in any way the tradition of the Apostolic Faith. I am of opinion that the Unjust Steward stands for the devil, who was sent into this world for the correction of mankind, so that we, flying from the malignant cruelty of this so evil steward might run together towards the compassion of God, through Whose power and mercy we can be delivered from every assault: and seeing that the steward is also subject to the power of the Lord God, Who as the Apostle teaches us, is rich unto all that call upon him. For Whosoever shall call upon the name of the Lord, shall be saved (Rom. X. 12).
And the devil wasted the substance of his Lord when he sought the ruin of mankind; that is, our death, who are the possession of God, as the Son of God bears witness, repeating by the mouth of the prophet the words of His Father; Ask of me, and I will give thee the Gentiles for thy inheritance, and the utmost parts of the earth for thy possession (Ps. ii. 8). And again: For the Lord had chose Jacob unto himself: Israel for his own possession (Ps. cxxxiv. 4). God seeing the insolence of the devil had become so great, that those he had been permitted to try, and solely for their correction, he had taken as his own, and put to death, now threatens him with expulsion so that his cruelty is broken through fear of unending punishment. And this most wicked one, reckoning the death of man as his profit, is consumed with anxiety because the Lord is about to take away his power over others. And since he is unable to will what is good and is ashamed to seek mercy through repentance, he thinks within himself how he may still have power over the debtors of his Lord (that is over those involved in the debt of sin), not alone by open persecution, but also, under the pretext of benevolence, by deceiving them with smooth words, so that seduced by his false kindness they may more readily receive him into their houses since together with him they must be judged for ever.
The devil believes that this would be a great alleviation of his torments, to secure many sharers of the penalties inflicted on himself. For the enemy, full of guile, and troubled by the Coming, and by the threat of Christ, thought within his one poisonous mind how even those who fled from him when he was persecuting them, may yet follow him should he give up something to them. He hastens to try these new schemes, and with different kinds of temptations he tries to undo men; power over whom he well knows will be wholly taken from him at the end of the world. For after the coming of Christ the devil was inflamed with redoubled fury against mankind; knowing that he hath but a short time (Apoc. Xii. 12), as was written of him. The debts of his fellow servants, which belong to his Lord he promises falsely to remit himself, when he offers an empty forgiveness to those who sin either in belief or in work; when he persuades them that the sins which they who commit them know are grievous sins will not be regarded as sins. For they confess the amount of their debt, since they know in their hearts they cannot deny their debt to God; for their contempt of His faith, and for the good they have failed to do. For they who render to God what is God’s are not God’s debtors. And do not be surprised that he lies about the forgiveness of their debts to men whom he is trying even more cunningly to destroy by this very deceit, since he dared to promise Christ, the Creator of all things, the kingdoms of this world, imprudently pretending they were his. All these are mind he says, and to whom I will I give them. If thou therefore will adore before me, all shall be thine (Lk. iv. 6, 7).
O the indescribable patience of Christ, Who suffered the tempter to speak in this way, that He might show us, whose humanity He has taken upon Himself the manner of fighting him and of defeating him! O the unbridled insolence of this liar the devil! He thinks Jesus is God, and yet tempts Him. He had reason to think that He was the Lord of all creation to Whom he lies that the kingdoms of the earth are his; and he promises that he will give possession of created things to Him by Whom he knew all things were made! For, as it was written: He was a murderer from the beginning, and he stood not in the truth, because the truth is not in him. (Jn viii. 44).
And now we come to the kinds of things of which there is question. The wheat as we said before, is the Faith of Christ; the beginning of life for man. For the bread of God is that which cometh down from heaven and giveth life to the world (Jn. vi. 33). And again He says: He that believeth in me, although he be dead, shall live (Jn. xi. 25). Oil stands for good works, and because the foolish virgins did not have any, the lamps of their souls were extinguished and they remained shut out in the darkness from the Chamber of the Bridegroom (heaven.) For our souls must not alone be virgin and untarnished; they must also ever carry in their vessels the oil of every good work; lest the lamp of faith go out for want of the oil of good works (Mt. xxv). For even as the body without the spirit is dead; so also faith without good works is dead (Jas. ii. 26).
The light of faith will then be steady and everlasting if it is nourished abundantly by the oil of good works. The devil therefore cheated mankind with false promises, so that they may disown their debt of faith and good works, until such time as they shall be thrust by the sentence of the Just judge into the prison of hell requiring of them that through torments they shall repay the last fathering (Mt. v. 25).
That he persuades them in place of a hundred barrels of oil, that is, of good works, to write fifty, and forces them to alter the debt of a hundred quarters of wheat to eighty, is more a veiled deception, a far more subtle snare of the enemy; which is when he involves those now withdrawn from the worship of idols in the various errors of heretical teachings, lessening the sum of their saving faith, and when he trips up those now turned away from evil practices, and eager to walk in the way of good works, by the eager desire to make known their good works. For he tries to pervert both our faith and our good works from the centenary number, that is from the number that stands for perfection, and which stands at the right-hand side: perverting the Apostolic Faith by the sinister interpretations of heretical teaching, and perverting the merit of our good works, of things done on the right-hand side, by leading us to a sinister way of life.
For how many has the devil not softened by his evil counsel, from the discipline of the right hand to the looseness of bodily pleasures? How many who were devout and eager in paying by good works the spiritual debts of religion has he not cheated of their heavenly reward, by infecting them with the desire of human glory, so that they may not receive the rewards promised to those on the right hand: for in their good works they now seek the good opinion of men rather than the praise and glory of God. And for this reason the Lord Christ the Son of God, warning His Disciples to be careful not to make known to men their uprightness, their alms, their fasting and praying, lest through the vain glory of the left-hand side they may not have the reward of the right hand, says to them: Let not they left hand know what thy right hand doth (Mt. vi. 3).
It is very plain to us then with what poisonous prudence this unjust steward alters the due debts of religion, transferring them from the right to the left hand side of the account. And it was not without prupose that the Lord, to Whom we ar indebted, suffered greater losses in His oil, by which our good works are signified, than in His wheat, placed before us as a figure of the Life-giving Faith. For he is less corrupted by the deceit of the devil who is led away from the true faith, than he who is led away from the practice of good works, as the Saviour bears witness: And why do you call me, Lord, Lord; and do not the things which I say? (Lk. vi. 46).
The Lord does not however praise him for goodness, nor for piety, nor for justice, but he praises the cunning, the artful prudence of the unjust steward; He praised him because he had prepared his fraud with such subtle evil. He praises him menacingly, and at the same praises him for acting prudently. Menacing, for by the very word unjust He condemns this most wicked prudence of the devil; He praises him as having acted prudently, while at the same time He prepares the minds of His listening Disciples against he subtle skill of his schemes, so that they may with all care, with all prudence, oppose those so cunning, this so evilly wise enemy. For the serpent was more subtle than any of the beasts of the earth (Gen. iii. 1), and he slew the men who were first made by the poisoned bite of his seduction. The bless Apostle making reference to the torturous character of the serpent says: We are not ignorant of his devices (II Cor. ii. 11). And for the same reason the Saviour also says: Be ye therefore wise as serpents and simple as doves (Mt. x. 16). And the Apostle Paul conveyed the same to us in different words when he said In malice be children, and in sense be perfect (I Cor. xiv, 20).
Christ bids us be prudent, but not venomous; wise, but not evil; and that putting off, like the snake, our old garment of sin, we are to be formed into a new man; protecting our Head, Which is Christ with ever care, and surrendering our members to be torn by the persecutors, that the Faith of Christ the Head of our salvation and of our Life, may remain sound and unwounded.
Accordingly, Beloved, let us imitate the prudence of this unjust steward, but not his perfidy. Let us imitate his cunning, but not his wickedness. As he was skilled in injuring others by his evil deeds, so must we be prepared in salutary knowledge, instructed and armed with all prudence; having on us the breastplate of faith, the helmet of salvation, the sword of the Spirit, and the impregnable shield of justice, by means of which we can, as the Apostle exhorts us, extinguish all the fiery darts of the most wicked one (Eph. vi. 16, 17); lest while we are unawares he may pierce us with the darts of his evil prompting; lest being unarmed he may overcome us; lest being asleep he should slay us; lest though armed and watching he should still defeat us, because we are not accustomed to fighting him. For the unclean spirits, whom the Lord calls the children of this world, that is the children of darkness are oftentimes more prudent than the children of light, whom God, Who is Light, has deigned to call to be His children by adoption, being born again through the mysteries of the heavenly Baptism. Farewell, Beloved in Christ. Amen.