Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing. For I testify again to every man that is circumcised, that he is a debtor to do the whole law. Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace. Galatians 5:2-4
When people think it is necessary for Christians to be circumcised and observe the worship laws of the Old Testament — such as resting on the Sabbath, observing the Jewish feast days, abstaining from certain foods, etc. — they fall from grace and lose the blessings that Christ won for them because they seek to be acceptable to God by their observance of the law. They fail to see that they must keep every demand of the law perfectly to be justified by it.
Grant that I trust in Your perfect righteousness alone and in Your sacrifice for my sins, O Christ, and not overthrow Your grace by seeking to be counted righteousness by my keeping of the law. Amen.
[Scripture quotations are from the King James Version of the Bible.]