Circumcision was very important for the Jews.  It was the sign of God's family promise which was originally given to Abraham (Genesis 17:1-14).  It was a constant reminder to every Jewish man and his wife that God would love, protect and bless His people if they were loyal to Him.  It was so important that Old Testament Jews would be excluded from God’s family if they were not circumcised (Genesis 17:14).  

The legalistic Jews had not understood that having God’s written law and performing the rituals was not the same as loving the Lord their God with all of their heart and soul and mind and strength (Mark 12:30).  Circumcision was only the sign of the covenant.  The Jewish-background believers needed to understand that their circumcision meant nothing if they disobeyed God.  On the other hand, uncircumcised Gentiles who did please God were behaving as true members of His family.  

Could anyone, whether or not they are circumcised, keep God’s law perfectly?  No!  Only Jesus could completely fulfil all the law (Matthew 5:17).  So, salvation could never come through circumcision.  However, when Jews became believers in Jesus, they claimed that their circumcision gave them a closer relationship with God than the Gentiles.  But really, they were no better than the Gentile believers.  Paul was saying that it is useless to rely on a sign of being obedient if their hearts and actions are disobedient.  

The same sort of thing can happen in our time in the church.  Some people assume that God will give them preferential treatment because they can see signs of godliness around them: a strong Christian family; grandparents or parents who served the Lord; going to church; baptism; attending communion; wearing a cross; fasting; working 'for the church'; giving money; helping the poor.  All these might indicate a commitment to Christ Jesus, but can just be rites, rituals or routine thoughts or actions.  Salvation does not come through any of them, but only by faith in Jesus Christ (Romans 3:22-23).  Perhaps we also forget that while human beings look at the outward appearance, the Lord looks at the heart (1 Samuel 16:7).  Does your devotion to the Lord match the external signs of belonging to Him and serving Him?  If not repent and start to obey what He says, today.