What, then, is true circumcision, and who are the true sons of Abraham?  Paul answers that vital question for the people of his time, and for those in our generation who have foolishly speculated that the people of Israel enjoy favor with God whether they obey His law or not.  Paul, a Hebrew of the Hebrews, will have nothing to do with such a delusive fantasy.  The true Jew, or the one who truly has the favor of God, is he who is a Jew inwardly, that is, in the heart.  His heart has been renewed, and he enjoys communion with God by faith in Christ.  The uncircumcised Gentile who has trusted in Christ possesses the true circumcision, because his heart has been circumcised, the evil heart of unbelief cut away and cast aside by the powerful operation of the Spirit of God. 

These last three phrases sum up the entire matter.  Genuine heart circumcision is a matter of the spirit.  God is not so much concerned with who our parents are, as what our spirits are like.  A Gentile walking in humble faith and obedience is accepted with Him, while a Jew who enjoys the privileges of the covenant, but slights those privileges to live in uncleanness, is no friend of God.  The Jew thought it was a mere matter “of the letter,” or his outward conformity to the law of God.  Paul is showing them that by the deeds of the law no flesh shall be justified in God’s sight.  External obedience is no substitute for genuine heart’s love, affection, and service.  The Jew by his external privileges and outward acts may earn the praise of his fellow men, but that is of no use.  It is the praise of God that the true believer seeks.  He whose heart has been circumcised, and who serves God with the spirit, will learn not to live for the praise of men, but for the praise of God, Who alone can give everlasting life.