Romans 2:13

For not the hearers of the law are just before God
The apostle here shows, that the Jews were justly condemned, notwithstanding their having and hearing of the law; since hearing without doing it, will never denominate persons righteous in the sight of God, however it might recommend them in the sight of men: regard seems to be had either to the first delivery of the law by Moses to the people of Israel, when he read it to them, and they hearkened to it, and promised obedience; or rather to the reading and hearing it every sabbath day; and may include a speculative knowledge of it, without a practical obedience to it; and which therefore must fall greatly short of entitling them to a justifying righteousness; since not these,

but the doers of the law, shall be justified;
by whom are meant, not such who merely literally and externally fulfil the law, as they imagine; for the law is spiritual, and regards the inward as well as the outward man, and requires internal holiness, as well as external obedience; and the apostle is speaking of justification before God, who sees the heart, and not before men, who judge according to outward appearance: nor are such designed who are imperfect doers of the law; for the law requires a perfect obedience, and what is not perfect is not properly righteousness; nor does it, nor can it consider an imperfect righteousness as a perfect one; for it accuses of, pronounces guilty, curses, and condemns for every transgression of it. But such only can be intended, who are doers of it spiritually, internally, as well as externally, and that perfectly. Adam, in his state of innocence, was a perfect doer of the law; he sinning, and all his posterity in him, none of them are righteous, but all pass under a sentence of condemnation. The best of men, even believers in Christ, are not without sin in themselves; and when any of the saints are said to be perfect, it must be understood in a comparative sense, or as they are considered in Christ. There never was but one since Adam, and that is Christ, who has fulfilled, or could perfectly fulfil the law; the thing is impossible and impracticable for fallen man: hence these words must be understood either hypothetically, thus, not the hearers of the law, but if there were any perfect doers of it, they would be justified before God; or else of such persons who are considered in Christ, by whom the whole perfect righteousness of the law is fulfilled in them, and who may be reckoned as perfect doers of it in him, their substitute, surety, and representative.