The interpretation timeline
1 Corinthians 9:19 Douay-Rheims

For whereas I was free as to all, I made myself the servant of all, that I might gain the more.

A.D. 215 – 1871 10 witnesses 13 excerpts

Patristic

before A.D. 750
215
A.D.
c. A.D. 150–215
“And especially is it incumbent on those entrusted with such a dispensation to exhibit to disciples a pure example. "For though I be free from all men, I have made myself servant to all," it is said, "that I might gain all. And every one that striveth for mastery is temperate in all things." "But the earth is the Lord's, and the fulness thereof." For conscience' sake, then, we are to abstain from what we ought to abstain. "Conscience, I say, not his own," for it is endued with knowledge, "but that of the other," lest he be trained badly, and by imitating in ignorance what he knows not, he become a despiser instead of a strong-minded man.”
Source
“For instance, Paul circumcised Timothy because of the Jews who believed, in order that those who had received their training from the law might not revolt from the faith through his breaking such points of the law as were understood more cam ally, knowing right well that circumcision does not justify; for he professed that "all things were for all" by conformity, preserving those of the dogmas that were essential, "that he might gain all." And Daniel, under the king of the Persians, wore "the chain," though he despised not the afflictions of the people.”
Source
“To illustrate: the noble apostle circumcised Timothy, though loudly declaring and writing that circumcision made with hands profits nothing. But that he might not, by dragging all at once away from the law to the circumcision of the heart through faith those of the Hebrews who were reluctant listeners, compel them to break away from the synagogue, he, "accommodating himself to the Jews, became a Jew that he might gain all." He, then, who submits to accommodate himself merely for the benefit of his neighbours, for the salvation of those for whose sake he accommodates himself, not partaking in any dissimulation through the perilimpending over the just from those who envy them, such an one by no means acts with compulsion. But for the benefit of his neighbours alone, he will do things which would not have been done by him primarily, if he did not do them on their account.”
Source
220
A.D.
Tertullian Patristic
c. A.D. 150–220
“Now by this time, you who argue about "Joseph" and "Daniel," know that things old and new, rude and polished, begun and developed, slavish and free, are not always comparable. For they, even by their circumstances, were slaves; but you, the slave of none, in so far as you are the slave of Christ alone, who has freed you likewise from the captivity of the world, will incur the duty of acting after your Lord's pattern.”
Source
“Ante-Nicene Fathers, Vol.”
407
A.D.
John Chrysostom Patristic
A.D. 347–407
“"For though I was free from all men, I brought myself under bondage to all, that I might gain the more." Here again he introduces another high step in advance. For a great thing it is even not to receive, but this which he is about to mention is much more than that. What then is it that he says? "Not only have I not received," saith he, "not only have I not used this right, but I have even made myself a slave, and in a slavery manifold and universal. For not in money alone, but, which was much more than money, in employments many and various have I made good this same rule: and I have made myself a slave when I was subject to none, having no necessity in any respect, (for this is the meaning of, "though I was free from all men;") and not to any single person have I been a slave, but to the whole world." Wherefore also he subjoined, "I brought myself under bondage to all." That is, "To preach the Gospel I was commanded, and to proclaim the things committed to my trust; but the contriving and devising numberless things beside, all that was of my own zeal. For I was only under obligation to invest the money, whereas I did every thing in order to get a return for it, attempting more than was commanded." Thus doing as he did all things of free choice and zeal and love to Christ, he had an insatiable desire for the salvation of mankind. Wherefore also he used to overpass by a very great deal the lines marked out, in every way springing higher than the very heaven.”
Source

Scholastic

c. 1100 – 1500
1270
A.D.
1225–1276
“Above he showed that he does not wish to accept expenses, and this on account of the intention of a reward; here he shows that he did the same thing on account of love of the Gospel. Where first he says that he made himself the servant of all; second, that he strove to accommodate himself to all, there "and I became to the Jews," etc.; third, he subjoins the reason why he did this, there "but all things I do on account of the Gospel," etc. In the first he implies a threefold commendable condition in servitude: which are generality, liberality, usefulness. He serves therefore freely or liberally, there "when I was free," etc.; generally, there "of all... me," etc.; usefully, there "that I might gain the more," etc. He says therefore "for when I was," etc., as if to say: I will set forth the Gospel without expense, for I have done even more, namely that although "I was free from all," etc., that is, obligated by no one's merits, "I made myself the servant of all," accommodating myself to all through lowliness, and as it were constituting myself a debtor — 2 Cor. 4:5: "but we are your servants through Jesus." And this "that I might gain the more," that is, that I might make a gain of my preaching and servitude. For he sought not things, but souls — 2 Cor. 12:14: "I seek not your things, but you." For if it is commendable to serve in temporal things for temporal gain, how much more in spiritual things for spiritual gain? Then, when he says "and I became to the Jews," etc., here he shows that he strove to accommodate himself to all. And first he says that he accommodated himself to those not yet converted; second, that also to those already converted, there "I became to the weak," etc.; third, that generally to all, there "I became all things to all," etc. In the first he first says that he accommodated himself to the Jews; second, that to the Samaritans, there "and to those who are under the law," etc.; third, that to the Gentiles, there "to those who were without the law," etc. In the first, he first touches the accommodation; second, the reason for the accommodation, there "that the Jews," etc. He says therefore: "and I became to the Jews as a Jew," namely by observing certain legal things, as in the distinction of foods, in the circumcision of Timothy, Acts 16:3, in the legal purification, Acts 21:24. But this can be understood in two ways. In one way, according to Jerome, "I became to the Jews as a Jew" through a dispensation of simulation — for he pretended to observe certain legal things, which nevertheless he did not observe. In another way, according to Augustine, "I became a Jew," etc. — for he truly condescended to them in the observance of certain legal things on account of pious compassion; and he did this that he might gain the Jews for Christ, that is, that he might convert them to the faith of Christ. Then, when he says "and to those who are under the law," etc., here he says that he was accommodating himself to the Samaritans. Where three things are noted about him: first, his sagacity in that he accommodated himself; second, his freedom in that he was not under the law; third, his usefulness in that he was gaining them. He says therefore: "I am also to those who are under the law of Moses," that is, to the Samaritans, who are not Jews but Assyrians, who were brought to inhabit the land of Israel, 4 Kings 17:24 ff. These also were under the law of Moses, because they received only the five books of Moses. To these therefore "I became as if I were under the law," namely by approving the law, and by teaching Christ from it, although "I myself was not under the law," according to literal observance, or servilely, because "the law is not laid down for the just man," 1 Tim. 1:9. And I did this therefore "that I might gain those who were under the law," namely the Samaritans themselves, by converting them to the faith of Christ. Then, when he says "to those who were without the law," etc., here he says that he accommodated himself to the Gentiles. Where first he touches his conformity; second, the truth of his faith, there "although without the law," etc.; third, the rectitude of his intention, there "that I might gain," etc. And this is: "and I became to those who were without the law," that is, to the Gentiles — Rom. 2:14: "for the Gentiles, who do not have the law" — "as if I were without law," that is, by assenting to their reasonings, and to the good positions of the philosophers, as is clear in Acts 17; "although I was not without law" — Rom. 7:25: "with the mind I serve the law of God" — "but I was in the law," not the Jewish law, but of Christ, who is God, and not Moses. Concerning which, Gal. 6:2: "bear one another's burdens, and thus you will fulfill," etc. And I did this therefore "that I might gain those who were without the law," by converting the Gentiles to the faith. O happy zealot! Gregory: "there is no sacrifice like the zeal of souls." Then, when he says "I became to the weak," etc., here he shows that he accommodated himself to those already converted. Where first he sets forth the good manner, second the due end, there "that the weak." He says therefore: "I became also to the weak," in faith, "weak," by abstaining from lawful things — 2 Cor. 11:29: "who is weak, and I am not weak?" So does the good physician, who eats the food of the sick man, that he may provoke him to eat, and so heal him. And this I did "that I might gain the weak," strengthening them in the faith. And briefly, "I became all things to all," as if I were of every sect. Therefore it is said below, 10:33: "as I also please all in all things." And this "that I might make all safe." In the ankle-length vestment which Aaron had, the whole world was depicted, Wisdom 18:24. And, 4 Kings 4:34, Elisha contracted himself to the manner of the boy, and thus revived him. And because, according to Boethius, every otherness is discordant, but likeness truly is to be sought, therefore spiritual men, saving the observance of their life and religion, ought to conform themselves to all. Then, when he says "all things I do on account of the Gospel," above he showed that he strove to accommodate himself to all; here he subjoins the reason why he does this, and this is twofold: one on the part of the Gospel, namely that it may have a free course; the other on his own part, namely that he may obtain the promised reward, there "that a partaker," etc. And this is what he says: "but all things I do on account of the Gospel," to be preached without impediment, "that I may become a partaker of it," that is, of the promises which are contained in it — Matt. 5:19: "whoever shall do and teach, he shall be called great in the kingdom of heaven."”

Reformation

c. 1500 – 1650
1637
A.D.
1567–1637
“For though I be free from all men, yet have I made myself servant unto all I humbled myself to all things, even to want and hunger ; I accommodated myself to the weaknesses of all, insomuch that, when I saw the Corinthians slow and niggardly in their support of the Apostles, I refused to accept any payment from them, that I might gain all by condescending to their infirmity”
Source

Post-Reformation

c. 1650 – 1900
1714
A.D.
Matthew Henry Reformed
1662–1714
“The apostle takes occasion from what he had before discoursed to mention some other instances of his self-denial and parting with his liberty for the benefit of others. I. He asserts his liberty (Co1 9:19): Though I be free from all men. He was free-born, a citizen of Rome. He was in bondage to none, nor depended upon any for his subsistence; yet he made himself a servant to all, that he might gain the more. He behaved as a servant; he laboured for their good as a servant; he was careful to please, as a servant to his master; he acted in many cases as if he had no privileges; and this that he might gain the more, or make the more converts to Christianity. He made himself a servant, that they might be made free. II. He specifies some particulars wherein he made himself a servant to all. He accommodated himself to all sorts of people. 1. To the Jews, and those under the law, he became a Jew, and as under the law, to gain them. Though he looked on the ceremonial law as a yoke taken off by Christ, yet in many instances he submitted to it, that he might work upon the Jews, remove their prejudices, prevail with them to hear the gospel, and win them over to Christ. 2. To those that are without the law as without law that is, to the Gentiles, whether converted to the Christian faith or not. In innocent things he could comply with people's usages or humours for their advantage. He would reason with the philosophers in their own way. And, as to converted Gentiles, he behaved among them as one that was not under the bondage of the Jewish laws, as he had asserted and maintained concerning them, though he did not act as a lawless person, but as one who was bound by the laws of Christ. He would transgress no laws of Christ to please or humour any man; but he would accommodate himself to all men, where he might do it lawfully, to gain some. Paul was the apostle of the Gentiles, and so, one would have thought, might have excused himself from complying with the Jews; and yet, to do them good, and win them over to Christ, he did, in innocent things, neglect the power he had to do otherwise, and conformed to some of their usages and laws. And though he might, by virtue of that character, have challenged authority over the Gentiles, yet he accommodated himself, as much as he innocently might, to their prejudices and ways of thinking. Doing good was the study and business of his life; and, so that he might reach this end, he did not stand on privileges and punctilios. 3. To the weak he became as weak, that he might gain the weak, Co1 9:22. He was willing to make the best of them. He did not despise nor judge them, but became as one of them, forbore to use his liberty for their sake, and was careful to lay no stumbling-block in their way. Where any, through the weakness of their understanding, or the strength of their prejudices, were likely to fall into sin, or fall off from the gospel into heathen idolatry, through his use of his liberty, he refrained himself. He denied himself for their sakes, that he might insinuate into their affections, and gain their souls. In short, he became all things to all men, that he might by all means (all lawful means) gain some. He would not sin against God to save the soul of his neighbour, but he would very cheerfully and readily deny himself. The rights of God he could not give up, but he might resign his own, and he very often did so for the good of others. III. He assigns his reason for acting in this manner (Co1 9:23): This I do for the gospel's sake, and that I may be partaker thereof with you; that is, for the honour of Christ, whose the gospel is, and for the salvation of souls, for which it was designed, and that he and they might communicate in the privileges of it, or partake together of them. For these ends did he thus condescend, deny himself as to his liberty, and accommodate himself to the capacities and usages of those with whom he had to do, where he lawfully might. Note, A heart warmed with zeal for God, and breathing after the salvation of men, will not plead and insist upon rights and privileges in bar to this design. Those manifestly abuse their power in the gospel who employ it not to edification but destruction, and therefore breathe nothing of its spirit.”
Source
1771
A.D.
John Gill Reformed
1697–1771
“And unto the Jews I became as a Jew,.... That is, in religion; or with respect to some religious observances peculiar to the Jews, for he himself was really a Jew by nature; who became as one unto them in this sense, when he for their sakes circumcised Timothy at Derbe, or Lystra, purified himself at Jerusalem, shaved his head at Cenchrea, observed their sabbath, and abstained from some sorts of food forbidden in the law; and his end in so doing was, not to confirm them in such usages, but that he might hereby have the greater influence over them, and by little and little bring them off of these things, or, as he says, that I might gain the Jews; bring them over to Christ, and off of a dependence on their own righteousness, for justification before God: to them that are under the law, as under the law; the Vulgate Latin version adds, "when I was not under the law", and so the Alexandrian copy and some others; by whom seem to be meant the same persons as before; though some have thought that the Samaritans are intended, and others the Sadducees: but if any as distinct from the former are designed, they should rather seem to be the converted Jews; who though they believed in Christ, looked upon themselves to be still under the law, and therefore observed it; with whom the apostle on certain occasions complied, as if he was under it too, that he might have the greater share in their affections and credit; hoping in time that by such means he might be able to prevail upon them to relinquish these things, and wholly attend to the Gospel and ordinances of Christ, or, as he says, that I might gain them that are under the law; meaning the Jews, who were observers of the law of Moses.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“For though I be free - Although I am under no obligation to any man, yet I act as if every individual had a particular property in me, and as if I were the slave of the public.”
1849
A.D.
1774–1849
“Free as to all. That is, whereas I was under no obligation to any man, yet I made myself the servant of all, &c. (Calmet)”
1871
A.D.
1871
“free from all men--that is, from the power of all men. gain the more--that is, as many of them ("all men") as possible. "Gain" is an appropriate expression in relation to a "reward" (Th1 2:19-20); he therefore repeats it frequently (Co1 9:20-22).”
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.