Romans 2:25 For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision. 26 Therefore if the uncircumcision keep the righteousness of the law, shall not his uncircumcision be counted for circumcision? 27 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?
James would tell us in his epistle that you either follow all of the law or none. You cannot claim to partially fulfill the law. God requires all or none.
James 2:10 For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.
In order for God to look favorably upon man for his works he must follow 100% of the law. Circumcision was not enough to stand before God. Just because you were of the blood of Abraham did not make you right with God. The Jews saw circumcision also connected to the law. It was a commandment from God. Paul is telling us how you must follow ALL of the law or you follow none of the law. It will all count against you if you fail in any point. Paul was showing that those who truly follow God follow all of His laws. He is giving an impossible task. Paul knows God did not give the law for us to follow to achieve access to Him. He gave the law to point us to Christ. No law, no circumcision was justification before God. Following the law is not possible with man. He wants their confidence in the law/circucision to be shaken. Paul says would that man who is not circumcised though he keep the law be justified before God? His point is following the law, physical circumcision, none of this can make you acceptable before God. Both Jew and Gentile are all in the same predicament. The Jews had a hard time accepting this fact. They stand upon the sand. There is no sturdy foothold in following the law. They need Christ the solid rock.