Romans 2:21

thou therefore that teacheth another, teachest thou not thyself? [But if doers, and not hearers, are not justified, why do you put your confidence in mere hearing, and such things as are analogous to it? Since only the doers of the law are justified, why do you vainly trust that you will be acceptable because you bear the proud name of Jew (Galatians 2:15; Philippians 3:5; Revelation 2:9), rather than the humble one of Gentile? Why do you rest confidently merely because you possess a better law than the Gentiles, because you glory in the worship of the true God (Deuteronomy 4:7), and in knowing his will (Psalms 147:19-20), and in being instructed so as to approve the more excellent things of the Jewish religion above the debauchery of idolatry? Of what avail are these things when God demands doing and not mere knowing? And of what profit is it to you if the law does give you such a correct knowledge of the truth that you are to the Gentiles, yea, even to their chief philosophers, as a guide to the blind, a light to the benighted, a wise man among fools, a skilled teacher among children? Of what avail or profit is it all if, with all this ability, you teach only others and fail to teach yourself? The apostle next shows, in detail, how truly the Jew had failed to profit by his knowledge, so as to become a doer of the law.] thou that preachest a man should not steal, dost thou steal?