Romans 2:19

"But if you are called a Jew, and rest in the law, and glory in God, and know his will, and approve the more useful things, being instructed by the law, and are confident that you are a guide of the blind, a light of those who are in darkness, an instructor of the foolish, a teacher of infants, having the form of knowledge and of truth in the law. You then who teach another, do you not teach yourself? You who preach that a man should not steal, do you steal?

"And art confident that thou thyself." Here again he does not say that thou art "a guide of the blind," but "thou art confident," so thou boastest, he says. So great was the unreasonableness of the Jews. Wherefore he also repeats nearly the very words, which they used in their boastings. See for instance what they say in the Gospels. "Thou wast altogether born in sin, and dost thou teach us?" (John ix. 34.) And all men they utterly looked down upon, to convince them of which, Paul keeps extolling them and lowering the others, that so he may get more hold on them, and make his accusation the weightier. Wherefore he goes on adding the like things, and making more of them by different ways of relating them. For "Thou art confident," he saith, "that thou thyself art a leader of the blind, An instructor of the foolish, a teacher of babes, which hast the form of knowledge and truth, which is in the Law." Here again he says not, in the conscience and in actions and in well-doings, but "in the Law;" and after saying so, he does here also what he did with regard to the Gentiles. For as there he says, "for wherein thou judgest another, thou condemnest thyself," so saith he here also.

For they become ridiculous even to the Gentiles themselves when, following the letter of the Law, they say: "Do not touch, do not taste, do not handle: all of which things are unto corruption according to the commandments and doctrines of men." But these things the Apostle indeed says to him who is a Jew in name, not in deed; yet they can pertain also to every man in whom there is only the name of religion and piety, while works, and knowledge, and faith are lacking. And therefore we ought to examine these matters with greater care in ourselves than in those who do not come to faith in Christ, lest any of us who through faith in Christ and through the circumcision given in baptism has been made a true Jew, and rests in the law of Christ, and boasts also that, having driven off the error of idols, he has come to know God and that His will has become known to him (for he knows how to prove what is good, and well-pleasing, and perfect, and has advanced so far that he is even a leader and teacher of the Church for enlightening those who are blind in knowledge, and for instructing the little ones in Christ) — lest, I say, such a man be willing indeed to teach others quite strictly, and to demand from those whom he instructs the highest discipline of chastity, while he himself is driven by the vice of intemperance and of covetousness, and sometimes even burns with the flames of hidden lust. To a man of this sort, then, this apostolic word is fittingly applied, saying to him: "You who teach another, do you not teach yourself? You who preach that a man should not steal, do you steal? […]

Above he said that hearing the law brings no benefit if doing it is not joined to it; "for not the hearers of the law," he says, "are righteous before God, but the doers of the law" (v. 13), now he says something greater, namely: …

Apply it, (1.) To the Jews in general. They thought themselves guides to the poor blind Gentiles that sat in darkness, were very proud of this, that whoever would have the knowledge of God must be beholden to them for it. All other nations must come to school to them, to learn what is good, and what the Lord requires; for they had the lively oracles.