10 So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants: we have done that which was our duty to do.
[AD 397] Ambrose of Milan on Luke 17:7-10
For we know that no one sits down before he has first passed over. Moses indeed also passed over, that he might see a great sight. Since then thou not only sayest to thy servant, Sit down to meat, but requirest from him another service, so in this life the Lord does not put up with the performance of one work and labour, because as long as we live we ought always to work. Therefore it follows, And will not rather say, Make ready wherewith I may sup.

Boast not thyself then that thou hast been a good servant. Thou hast done what thou oughtest to have done. The sun obeys, the moon submits herself, the angels are subject; let us not then seek praise from ourselves. Therefore He adds in conclusion, So likewise ye, when ye have done all good things, say, We are unprofitable servants, we have done that which it was our duty to do.

[AD 397] Ambrose of Milan on Luke 17:7-10
You do not say to your servant, “Sit down,” but require more service from him and do not thank him. The Lord also does not allow only one work or labor for you, because so long as we live we must always work.Know that you are a servant overwhelmed by very much obedience. You must not set yourself first, because you are called a son of God. Grace must be acknowledged, but nature not overlooked. Do not boast of yourself if you have served well, as you should have done. The sun obeys, the moon complies, and the angels serve.… Let us not require praise from ourselves nor prevent the judgment of God and anticipate the sentence of the Judge but reserve it for its own time and Judge.

[AD 407] John Chrysostom on Luke 17:7-10
The mulberry may be also compared to the devil, for as by the leaves of the mulberry tree certain worms are fed, so the devil, by the imaginations which proceed from him, is feeding for us a never dying worm; but this mulberry tree faith is able to pluck out of our souls, and plunge it into the deep.

[AD 407] John Chrysostom on Luke 17:7-10
He said, “When you have done everything, say, ‘We are unprofitable servants,’ ” to warn them in his wish that they keep themselves at great distance from that destructive passion. Dearly beloved, see how the person with his mouth open for human glory and performing the works of virtue on that account has no benefit from it. Despite practicing every example of virtue, if he seems to give himself credit for it, he ends up empty-handed and bereaved of everything.

[AD 430] Augustine of Hippo on Luke 17:7-10
(de Quæst. Ev. l. 2. qu. 39.) Or else; To the many who understand not this faith in the truth already present, our Lord might seem not to have answered the petitions of His disciples. And there appears a difficulty in the connection here, unless we suppose He meant the change from faith to faith, from that faith, namely, by which we serve God, to that whereby we enjoy Him. For then will our faith be increased when we first believe the word preached, next the reality present. But that joyful contemplation possesseth perfect peace, which is given unto us in the everlasting kingdom of God. And that perfect peace is the reward of those righteous labours, which are performed in the administration of the Church. Be then the servant in the field ploughing, or feeding, that is, in this life either following his worldly business, or serving foolish men, as it were cattle, he must after his labours return home, that is, be united to the Church.

(de Quæst. Ev. ubi sup.) While His servants also are ministering, that is, preaching the Gospel, our Lord is eating and drinking the faith and confession of the Gentiles. It follows, And afterward thou shall eat and drink. As if He says, After that I have been delighted with the work of thy preaching, and refreshed myself with the choice food of thy compunction, then at length shalt thou go, and feast thyself everlastingly with the eternal banquet of wisdom.

[AD 444] Cyril of Alexandria on Luke 17:7-10
Our Lord teaches us that it is no more than the just and proper right of a master to require, as their bounden duty, subjection from servants, adding, Doth he thank that servant because he did the things that were commanded him? I trow not. Here then is the disease of pride cut away. Why boastest thou thyself? Dost thou know that if thou payest not thy debt, danger is at hand, but if thou payest, thou doest nothing thankworthy? As St. Paul says, For though I preach the Gospel I have nothing to glory of, for necessity is laid upon me, yea, woe is unto me if I preach not the Gospel. (1 Cor. 9:16.)
Observe then that they who have rule among us, do not thank their subjects, when they perform their appointed service, but by kindness gaining the affections of their people, breed in them a greater eagerness to serve them. So likewise God requires from us that we should wait upon Him as His servants, but because He is merciful, and of great goodness, He promises reward to them that work, and the greatness of His loving-kindness far exceeds the labours of His servants.

[AD 735] Bede on Luke 17:7-10
Or the servant departs from the field when giving up for a time his work of preaching, the teacher retires into his own conscience, pondering his own words or deeds within himself. To whom our Lord does not at once say, Go from this mortal life, and sit down to meat, that is, refresh thyself in the everlasting resting-place of a blessed life.

He bids make ready wherewith he may sup, that is, after the labours of public discourse, He bids him humble himself in self-examination. With such a supper our Lord desires to be fed. But to gird one's self is to collect the mind which has been enfolded in the base coil of fluctuating thoughts, whereby its steps in the cause of good works are wont to be entangled. For he who girds up his garments does so, that in walking he may not be tripped up. But to minister unto God, is to acknowledge that we have no strength without the help of His grace.

Servants, I say, because bought with a price; (1 Cor. 6:20) unprofitable, for the Lord needeth not our good things, (Ps. 16:2) or because the sufferings of this present time are not worthy to be compared to the glory which shall be revealed in us. (Rom. 8:18.) Herein then is the perfect faith of men, when having done all things which were commanded them, they acknowledge themselves to be imperfect.

[AD 1107] Theophylact of Ohrid on Luke 17:7-10
Because faith makes its possessor a keeper of God's commandments, and adorns him with wonderful works; it would seem from thence that a man might thereby fall into the sin of pride. Our Lord therefore forewarned His Apostles by a fit example, not to boast themselves in their virtues, saying, But which of you having a servant plowing, &c.

[AD 108] Ignatius of Antioch on Luke 17:10
And again, "When ye shall have done all things that are commanded you, say, We are unprofitable servants; "
[AD 258] Cyprian on Luke 17:10
But some who are of the lapsed have lately written to me, and are humble and meek and trembling and fearing God, and who have always laboured in the Church gloriously and liberally, and who have never made a boast of their labour to the Lord, knowing that He has said, "When ye shall have done all these things, say, We are unprofitable servants: we have done that which was our duty to do." Thinking of which things, and although they had received certificates from the martyrs, nevertheless, that their satisfaction might be admitted by the Lord, these persons beseeching have written to me that they acknowledge their sin, and are truly repentant, and do not hurry rashly or importunately to secure peace; but that they are waiting for my presence, saying that even peace itself, if they should receive it when I was present, would be sweeter to them. How greatly I congratulate these, the Lord is my witness, who hath condescended to tell what such, and such sort of servants deserve of His kindness. Which letters, as I lately received, and now read that yon have written very differently, I beg that you will discriminate between your wishes; and whoever you are who have sent this letter, add your names to the certificate, and transmit the certificate to me with your several names. For I must first know to whom I have to reply; then I will respond to each of the matters that you have written, having regard to the mediocrity of my place and conduct. I bid you, beloved brethren, ever heartily farewell, and live quietly and tranquilly according to the Lord's discipline.

[AD 735] Bede on Luke 17:10
What we ought to have done, we have done. Indeed we ought to have, because he who did not come to be served, but to serve (Matt. 20), made us debtors to himself, so that, evidently not trusting in our own works, but always fearing his judgment, we may say with the prophet: What shall we render to the Lord for all that he has rendered to us? (Psalm 115). In order to show that he had faith like a mustard seed, humble and fervent, he prefaced, saying: I believed, therefore I have spoken, but I was greatly humbled (Psalm 116). To show that he did not trust in his own strength, he added, speaking in ecstasy: Every man is a liar (Psalm 116), to signify himself as an unworthy servant even after receiving the precious chalice of death, he exclaimed: O Lord, I am your servant, I am your servant, and the son of your handmaid, you have loosed my bonds (Psalm 116). He did not say, I have loosed them myself, I am sufficient to save myself, but You have loosed my bonds, I will offer to you the sacrifice of thanksgiving (Psalm 116). This then is the only perfection of faith in men, if, having fulfilled everything that has been commanded, they know themselves to be imperfect, and as long as they wander away from the Lord, always acknowledge the evils in themselves to lament, always remember the good that is missing that, with his grace aiding, they may progress.