Romans 2:17-25 :
Indeed you bear the name of a Jew, and rest on the law, and glory in God, and know his will, and approve the things that are excellent, being instructed out of the law, and are confident that you yourself are a guide of the blind, a light to those who are in darkness, a corrector of the foolish, a teacher of babies, having in the law the form of knowledge and of the truth. You therefore who teach another, don’t you teach yourself? You who preach that a man shouldn’t steal, do you steal? You who say a man shouldn’t commit adultery. Do you commit adultery? You who abhor idols, do you rob temples? You who glory in the law, through your disobedience of the law do you dishonor God? For “the name of God is blasphemed among the Gentiles because of you,” just as it is written. For circumcision indeed profits, if you are a doer of the law, but if you are a transgressor of the law, your circumcision has become uncircumcision.
Just because a person knows about religion doesn’t mean that they are religious. A person is only religious if they do what God says they are supposed to do. If a person does what God wants, even if they don’t claim to be religious, they are acting religiously.
If a person claims to be religious and goes around sinning, that person makes a mockery of their religion. That is what God was accusing the Jews of here, but the same could be said about any person who claims to be religious. If you claim to be religious and don’t do what you are supposed to do, you are making a mockery of what you say you believe. It doesn’t matter what you say to people, or what memberships you have, if you don’t do religious things, then you are not religious.
Paul knew that the only true religion was found in The Rules of the Old Testament and no one has been able to do that without depending on sacrifices for sin. There is more about this later in Romans.
The fact is, Christians aren’t able to be religious by rule following either. We are only able to do what God wants when we trust in His power while believing and doing what He says. It isn’t a performance it is dependence. Only when we depend on Him are we be able to practice what we preach.