Romans 2:28-29 KJV
For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:
But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
This has forever been a point of trouble for the Jew.
• After centuries, even millennia being trained in the importance of outward traditions; especially in that of circumcision.
• After reading of Moses' confrontation before God because his sons had not been circumcised and of Israel's mass rite of circumcision on the banks of Jordan prior to entering into the Promised Land
to now be told that the physical rite isn't as important as the spiritual one: no wonder this is hard for the Jew to swallow even today.
And though it is a genuine struggle for the Jew, it is also a representative struggle between the spirit and the flesh in the Gentile believer. Everything in us wants to keep religion in the realm of the flesh precisely because it is easier than dealing with matters of the heart.
Mind you, this in no way excuses us from deep obedience to God in the flesh. But it urges us to learn a new motive for that obedience; it is to be stirred up from the working of the Spirit of God within us. It is to be the result of a "circumcised heart" and not from the flesh's attempt to earn favor with God.