The interpretation timeline
Galatians 2:16 Douay-Rheims

But knowing that man is not justified by the works of the law, but by the faith of Jesus Christ; we also believe in Christ Jesus, that we may be justified by the faith of Christ, and not by the works of the law: because by the works of the law no flesh shall be justified.

A.D. 220 – 1871 9 witnesses 10 excerpts

Patristic

before A.D. 750
220
A.D.
Tertullian Patristic
c. A.D. 150–220
“But what do the Marcionites wish to have believed (on the point)? For the rest, the apostle must (be permitted to) go on with his own statement, wherein he says that "a man is not justified by the works of the law, but by faith: " faith, however, in the same God to whom belongs the law also. For he remembered that the time was come of which the Psalm spake, "Let us break their bands asunder, and cast off their yoke from us; " since the time when "the nations became tumultuous, and the people imagined vain counsels; "when "the kings of the earth stood up, and the rulers were gathered together against the Lord, and against His Christ," in order that thenceforward man might be justified by the liberty of faith, not by servitude to the law, "because the just shall live by his faith.”
Source
407
A.D.
John Chrysostom Patristic
A.D. 347–407
“"Knowing that a man is not justified by the works of the Law, save through faith, in Jesus Christ, even we believed on Christ Jesus." Observe here too how cautiously he expresses himself; he does not say that they had abandoned the Law as evil, but as weak. If the law cannot confer righteousness, it follows that circumcision is superfluous; and so far he now proves; but he proceeds to show that it is not only superfluous but dangerous. It deserves especial notice, how at the outset he says that a man is not justified by the works of the Law; but as he proceeds he speaks more strongly.”
Source

Scholastic

c. 1100 – 1500
1273
A.D.
Thomas Aquinas Catholic
1225–1274
“Above he showed the truth of the apostolic doctrine preached by him, from the authority of the other apostles; here he shows the same thing from their manner of life and example. And concerning this he does two things. First he shows his proposition through the manner of life of the apostles; second, the objection of adversaries, that "if, seeking to be justified," etc. Concerning the first he does three things. First he sets forth beforehand the condition of the apostles; second he touches upon their manner of life, at the place "but knowing that a man is not justified," etc.; third, the condition intended, at the place "wherefore by the works of the law," etc. Now the condition of the apostles, and also of Paul himself, is this: that according to natural origin they proceeded from the Jews. And this is what he says: "we," namely I and the other apostles, "are by nature," that is, by natural origin, "Jews," not proselytes. 2 Corinthians 11:22: "They are Hebrews, so am I," etc. And this is great praise, because, as is said in John 4:22, salvation is from the Jews. And "not sinners of the Gentiles," that is, we are not sinners, as the idolatrous and unclean Gentiles are. But against this is what is said in 1 John 1:8: "If we shall say that we have no sin," etc.; therefore the Jews are sinners. I respond. It must be said that to be sinning is one thing, to be a sinner another. For the first denominates an act, but the second a readiness, or habit, toward sinning. Whence Scripture is accustomed to call the wicked, and those burdened with grave loads of sins, "sinners." The Jews, therefore, growing proud on account of the law, as it were restrained by it from sins, called the Gentiles, who were without the rein of the law and prone to sin, "sinners." Ephesians 4:14: "let us not be carried about by every wind of doctrine," etc. When therefore the Apostle says "not sinners of the Gentiles," it is explained thus: that is, we are not of the number of the sinners who are among the Gentiles, etc. Consequently, when he says "but knowing that a man is not justified," etc., he sets forth the manner of life of the apostles, which indeed is not in the things of the law, but in the faith of Christ. And concerning this he does two things. First he expresses the reason for the apostolic manner of life; second he sets forth the apostolic manner of life itself, at the place "and we in Christ," etc. The apostolic manner of life, then, was in faith, and not in the things of the law. The reason for this is that although we were Jews by nature and nourished in the things of the law, nevertheless, knowing for certain that a man is not justified by the works of the law, that is, through the legal works, except through the faith of Jesus Christ, therefore, forsaking those things, we conduct our lives in the precepts of faith. Romans 3:28: "For we reckon a man to be justified by faith without the works of the law." Acts 4:12: "there is no other name," etc. But against this: for in Romans 2:13 it is said: "For not the hearers of the law are just before God, but the doers of the law shall be justified," etc. It seems, therefore, that a man is justified by the works of the law. I respond. It must be said that "to be justified" can be taken in two ways: namely, to carry out justice, and to become just. Now in the first way, a man is justified who does works of justice. But no one becomes just except from God, through grace. It must be known, therefore, that of the works of the law, some were moral, and some indeed ceremonial. But the moral works, although they were contained in the law, nevertheless could not properly be called "works of the law," since man is led to them by natural instinct, and by the natural law. But the ceremonial works are properly called "works of the law." However much, therefore, a man is justified — as regards the carrying out of justice — by the moral works, and also by the ceremonial works, insofar as to observe them is a work of obedience, so far as they pertain to the sacraments; and it is taken in this way according to the saying of the Apostle in Romans 2:13. As to becoming just, however, a man is seen not to be justified by these, from the works of the law, because the sacraments of the old law did not confer grace. Below, 4:9: "you are turned again to the weak elements," that is, elements not conferring grace, nor containing grace in themselves. But the sacraments of the new law, although they are material elements, are nevertheless not weak elements, because they contain grace in themselves, whence they are also able to justify. But if any in the old law were just, they were not just from the works of the law, but only from the faith of Christ, whom God set forth as a propitiator through faith, as is said in Romans 3:20. Whence also the sacraments themselves of the old law were nothing but certain professions of the faith of Christ, just as our sacraments also are; but differently, because those sacraments configured the grace of Christ as it were future; but our sacraments make profession as containing, as it were, present grace. And therefore he says pointedly, that a man is not justified by the works of the law, except through the faith of Jesus Christ, because even if formerly some who kept the works of the law were justified, this nevertheless was not except through the faith of Jesus Christ. Now from this knowledge which the apostles had, that justification is not through the working of the law, but through the faith of Christ, he concludes the manner of life of the apostles, choosing the faith of Christ and leaving aside the works of the law. Whence there follows, "and we believe in Christ Jesus," because, as is said in Acts 4:12, "there is no other name given," etc. Whence there follows, "that we may be justified by the faith of Christ." Romans 5:1: "Being justified therefore by faith," etc. And lest anyone believe that, together with the law of Christ, the works of the law also justify, he adds, "and not by the works of the law." Romans 3:28: "For we reckon that a man is justified by faith," etc. From this he concludes the principal point intended, saying that if the apostles, who are Jews by nature, do not seek to be justified through the works of the law, but through faith, that "no flesh is justified by the works of the law," nor can any man whatsoever be justified through the works of the law. For here "flesh" is taken for man, namely a part for the whole, as in Isaiah 40: "all flesh shall see the salvation of our God." But in saying "wherefore," etc., he concludes as it were from the greater. For it seems more natural or reasonable that the Jews, rather than others, should be justified through the works of the law, not through faith; but this is not so: wherefore, etc.”

Reformation

c. 1500 – 1650
1637
A.D.
1567–1637
“A man is not justified by the works of the law , but by the faith of Jesus Christ, The English but here exactly interprets the work that the Latin translates by nisi. There is an antithesis between the works of the law and the faith of Jesus Christy and accordingly the Protestants are wrong in neglecting the force of the antithesis, and translating the phrase as if it meant a man is justified only by the faith of Christ, Moreover, even if the Apostle had said the latter, yet he would lend no support to the Protestant doctrine of justification by faith only, for S. Thomas admits faith as the sole justifying cause. The word only excludes the works of the law, not the works of hope, fear, charity, and penance, which spring from faith as daughters from a mother”
Source

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“Knowing that a man is not justified by the works of the law,.... That is, Peter, Paul, Barnabas, and other believing Jews knew this, and that from the law itself, which requires perfect and sinless obedience, and accuses, holds guilty, and adjudges to condemnation and death for the least failure, both as to matter or manner of duty; and from the prophets, which declare that by the deeds of the law no flesh can be justified in the sight of God, and who bear witness to the doctrines of remission of sin, and justification by the righteousness of Christ; and from the Gospel, in which this truth is most clearly revealed; and from the illumination of the blessed Spirit, who led them into all truth; and from the revelation of Jesus Christ they were favoured with; and from their own experience, being fully convinced of the exceeding sinfulness of sin, the insufficiency of their own righteousness, and of the necessity, suitableness, and fulness of the righteousness of Christ. By "the works of the law" are meant, not only obedience to the ceremonial law, though this is included, but also to the moral law; for it can hardly be thought, that the men the apostle opposes could ever dream of justification by their compliance with the rituals of the ceremonial law if they believed there could be no justification by their obedience to the moral law; for if there is no justification by the latter, there can be none by the former: the words are therefore to be taken in the largest sense, as rejecting all works of the law, of whatsoever kind, from justification in the sight of God; and such works are designed, as are performed by sinful men in and of themselves, otherwise men are justified by the works of the law as performed by Christ in their room and stead, but not by any as performed by themselves, for at best they are very imperfect, and so cannot justify; they are opposed to the grace of God, to which the justification of a sinner is always ascribed, and therefore cannot be by works; such a scheme would disannul the death of Christ, and promote boasting in men, and indeed is impracticable and impossible: but by the faith of Jesus Christ; not by that faith, which Christ, as man, had in God, who promised him help, succour, and assistance, and for which he, as man, trusted in him, and exercised faith upon him; but that faith of which he is the object, author, and finisher; and not by that as a cause, for faith has no causal influence on the justification of a sinner; it is not the efficient cause, for it is God that justifies; nor the moving cause, or which induces God to justify any, for that is his own free grace and good will; nor the meritorious or procuring cause, for that is the obedience and bloodshed of Christ; nor is faith the matter of justification; it is not a justifying righteousness; it is a part of sanctification; it is imperfect; as an act it is a man's own, and will not continue for ever in its present form, nature, and use; and is always distinguished from the righteousness of God, by which we are justified, which is perfect, is another's, and will last for ever. Men are not justified by faith, either as an habit, or an act; not by it as an habit or principle, this would be to confound justification and sanctification; nor as an act, for as such it is a man's own, and then justification would be by a man's works, contrary to the Scripture: but faith is to be taken either objectively, as it relates to Christ, the object of it, and his justifying righteousness; or as it is a means of receiving and apprehending Christ's righteousness; the discovery of it is made to faith; that grace discerns the excellency and suitableness of it, approves of it, rejects a man's own, lays hold on this, and rejoices in it: even we have believed in Jesus Christ; we who are Jews by nature, being fully apprized that there is no justification by the works of the law, but by the righteousness of Christ, received by faith, have quited all confidence in our own works, and are come to Christ, and believe in him, not only as the Messiah, but as the Lord our righteousness: that we might be justified by the faith of Christ, and not by the works of the law; not that faith, as before observed, has any causal influence on justification. These Jews did not believe in Christ, in order by their believing to procure their justification before God, and acceptance with him, but that they might receive, by faith, this blessing from the Lord in their own conscience, and enjoy the comfort of it, and all that spiritual peace which results from it, and which they could not find in the works of the law: for by the works of the law shall no flesh be justified; reference seems to be had to Psa 143:2 and contains a reason why these believing Jews relinquished Moses in his law, in whom they formerly trusted, and looked to, and depended on for their justification, because that by obedience to the law of works no sinful mortal man can be justified in the sight of God,”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“Knowing that a man is not justified - See the notes on Rom 1:17; Rom 3:24 (note), Rom 3:27 (note); Rom 8:3 (note). And see on Act 13:38 (note) and Act 13:39 (note), in which places the subject of this verse is largely discussed. Neither the works of the Jewish law, nor of any other law, could justify any man; and if justification or pardon could not have been attained in some other way, the world must have perished. Justification by faith, in the boundless mercy of God, is as reasonable as it is Scriptural and necessary.”
Source
1849
A.D.
1774–1849
“&c. Knowing that a man is not justified by the works of the law. St. Paul, to the end of the chapter, seems to continue his discourse to St. Peter, but chiefly to the Jewish Galatians, to shew that both the Gentiles, whom the Jews called and looked upon as sinners, and also the Jews, when converted, could only hope to be justified and saved by the faith of Christ, and not by the works of the law. — But if while we seek to be justified in Christ, by faith in him, and by his grace, we ourselves also are found sinners, as the false doctors teach you, and not to be justified but by the ceremonies and works of the law of Moses, this blasphemous consequence must follow, that Christ is the minister and author of sin, by making us believe that by faith in him, and complying with his doctrine, we may be justified and saved. For thus we must be considered transgressors, unless we renew and build again what Christ and we have destroyed. — For by the law I am dead to the law. That is, says St. Jerome, by the evangelical law of Christ I am dead to the ancient law and its ceremonies. Others expound it, that by the law and its types and figures, and by the predictions contained in the law, I know the Mosaical law hath now ceased, in which sense he might say, by the law I am dead to the law. — If justice. That is, if justification and salvation be to be had, or could have been had by the works of the law; therefore Christ died in vain, and it was not necessary that he should become our Redeemer. (Witham)”
Source
1863
A.D.
1796–1863
“The article is wanting ; but the Mosaic law is often designated without the article, as Winer observes. The text, however, might be understood of law gene- rally, since justification is not attainable by any works of any law, but through faith with the other dispositions which proceed from it.”
“Rom. iii. 20. By legal works.”
1871
A.D.
1871
“not justified by the works of the law--as the GROUND of justification. "The works of the law" are those which have the law for their object--which are wrought to fulfil the law [ALFORD]. but by--Translate, "But only (in no other way save) through faith in Jesus Christ," as the MEAN and instrument of justification. Jesus Christ--In the second case, read with the oldest manuscripts, "Christ Jesus," the Messiahship coming into prominence in the case of Jewish believers, as "Jesus" does in the first case, referring to the general proposition. justified by the faith of Christ--that is, by Christ, the object of faith, as the ground of our justification. for by the works of the law shall no flesh be justified--He rests his argument on this as an axiom in theology, referring to Psa 143:2, "Moses and Jesus Christ; The law and the promise; Doing and believing; Works and faith; Wages and the gift; The curse and the blessing--are represented as diametrically opposed" [BENGEL]. The moral law is, in respect to justification, more legal than the ceremonial, which was an elementary and preliminary Gospel: So "Sinai" (Gal 4:24), which is more famed for the Decalogue than for the ceremonial law, is made pre-eminently the type of legal bondage. Thus, justification by the law, whether the moral or ceremonial, is excluded (Rom 3:20).”
Source
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.