Romans 2:23 (KJV)

And knowest his will, and approvest the things that are more excellent, being instructed out of the law;

And art confident that thou thyself art a guide of the blind, a light of them which are in darkness,

An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law.

Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal?

Thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou commit sacrilege?

For the name of God is blasphemed among the Gentiles through you, as it is written.

For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision.

Therefore if the uncircumcision keep the righteousness of the law, shall not his uncircumcision be counted for circumcision?

And shall not uncircumcision which is by nature, if it fulfil the law, judge thee, who by the letter and circumcision dost transgress the law?

For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: