Even today as Christians, it is easy to replace the true intent of scripture for something man made. We readily assign rituals and regulations to follow in the name of Christ in order to ignore the objective of our heart behind it. It is easy to look at the natural realm of religion and therefore separate ourselves from relationship with God. To avoid this, we have to keep our heart in check.
Today's passage of scripture is powerful. Paul is saying that the condition of the heart is what makes someone a Jew, or part of God's chosen people... "A man is not a Jew if he is only one outwardly, nor is circumcision merely outward and physical." ( Romans 2:28 ) Paul is saying that circumcision is an outward sign of an inward reality. It is the condition of ones heart that makes them a child of God.
Circumcision dates back to Abraham, but Abraham received the mark of circumcision as a token or as evidence of the righteousness he had through faith before he was circumcised. That righteousness did not come by observing the Law because it was given before the Law was put into effect. His righteousness came from Faith, and his circumcision was a symbol of that faith. ( Romans 4:11-13 ) Therefore circumcision has always been a sign of the condition of the heart, but the Jews forsook the intent and focused all of their attention on the physical aspect of it.
Therefore Paul is clarifying that being a Jew is not because you were born into that nationality or religion. Being of God's chosen people comes through circumcision of the heart, which is spiritual rather than natural. This spiritual transformation comes about by being united with Christ and born again. It is by the Spirit that this happens not by the written code. Galatians 3:29 says, "If you belong to Christ, then you are Abraham's seed, and heirs according to the promise." This leaves no doubt that the church is now God's chosen people on earth. Both Jews and Gentiles who have put their Faith in Jesus are part of the kingdom of God, our 'circumcision is of the heart, by the Spirit'.
Today, by believing in Jesus and putting your faith alone in Him, you have the circumcision of Christ. "In him you were also circumcised, in the putting off of the sinful nature, not with a circumcision done by the hands of men but with the circumcision done by Christ..." ( Colossians 2:11 ) This is the true mark of a child of God. Amen and So Be it!