SIGN OF THE NEW COVENANT
It is important to review this history of Jewish circumcision because it is tied to the covenant between God and Abraham that is the basis of all of the rest of the Bible. It is also important because Abraham’s circumcision is referenced in the New Covenant. But we do not need to wait to read about that in the New Testament because it appears in the following Old Testament scriptures.

Deuteronomy 10:16 RSV Circumcise therefore the foreskin of your heart, and be no longer stubborn.
COMMENTARY: Here we have the explanation for a spiritual circumcision. The fact that it appears in one of the books of the Law of Moses suggests that the terms of the law were symbolic and not meant to be taken literally. This helps us to accept that large-scale circumcision events in previous scriptures were spiritual and not physical.
This scripture provides the first clues that references to the heart are code words about the New Covenant. It anticipates Jeremiah 31:31-34
Deuteronomy 30:6 RSV And the LORD your God will circumcise your heart and the heart of your offspring, so that you will love the LORD your God with all your heart and with all your soul, that you may live.

COMMENTARY: This is another scripture that strongly suggests that earlier commandments in the Law of Moses were symbolic representations of spiritual events. Clearly God is doing the work here and it is done on the heart — not on the flesh.

We also get our first clue that circumcision is related to the New Covenant. References to the heart always point to the New Covenant because the New Covenant provides that the law will be written on the hearts of men.

This scripture says that a New Covenant relationship with God was always possible — even in the time of Moses. This fact spoils the common assumption that the New Covenant was established only after Jesus’ death and resurrection. The New Covenant was, in fact, always available as the spiritual alternative to the literal Law of Moses. More to the point, it was always the desired covenant from God’s perspective.

What this says about circumcision is that God was always looking for people who would be circumcised in their hearts. Circumcision of the flesh was, and is, only a symbolic representation of circumcision of the heart.

Joshua 5:1-7 RSV When all the kings of the Amorites that were beyond the Jordan to the west, and all the kings of the Canaanites that were by the sea, heard that the LORD had dried up the waters of the Jordan for the people of Israel until they had crossed over, their heart melted, and there was no longer any spirit in them, because of the people of Israel. 2 At that time the LORD said to Joshua, “Make flint knives and circumcise the people of Israel again the second time.” 3 So Joshua made flint knives, and circumcised the people of Israel at Gibeath-haaraloth. 4 And this is the reason why Joshua circumcised them: all the males of the people who came out of Egypt, all the men of war, had died on the way in the wilderness after they had come out of Egypt. 5 Though all the people who came out had been circumcised, yet all the people that were born on the way in the wilderness after they had come out of Egypt had not been circumcised. 6 For the people of Israel walked forty years in the wilderness, till all the nation, the men of war that came forth out of Egypt, perished, because they did not hearken to the voice of the LORD; to them the LORD swore that he would not let them see the land which the LORD had sworn to their fathers to give us, a land flowing with milk and honey. 7 So it was their children, whom he raised up in their stead, that Joshua circumcised; for they were uncircumcised, because they had not been circumcised on the way.

COMMENTARY: These verses continue to reinforce circumcision of the heart as a New Covenant feature. Joshua is a type of Christ who leads Israel into the Promised Land which is a literary term for the New Covenant. This story about Joshua prophetically forecasts Jesus leading both Jews and Gentiles into the Promised Land.

The command to circumcise the people before entering the Promised Land is God’s way of saying that the law must be written on the hearts of the people before they can enter into the New Covenant relationship with God. But it is a command to circumcise the heart and ear — not the flesh.

Jeremiah 6:8-10 KJV: Be thou instructed , O Jerusalem, lest my soul depart from thee; lest I make thee desolate, a land not inhabited . 9 Thus saith the LORD of hosts, They shall thoroughly glean the remnant of Israel as a vine: turn back thine hand as a grape gatherer into the baskets. 10 To whom shall I speak, and give warning , that they may hear? Behold, their ear is uncircumcised, and they cannot hearken: behold, the word of the LORD is unto them a reproach; they have no delight in it.

COMMENTARY: In this scripture, circumcision is equated with the ability to hear. God is warning people who cannot hear that they will be reproached for their inability to hear his word and delight in it.

Jeremiah is full of such warnings to Israel. They are all preambles to Jeremiah 31:31-34 which contains God’s clear promise to usher his people into New Covenant status. Thus, people with uncircumcised ears are equated to Old/First Covenant believers with uncircumcised hearts. They can hear and read God’s literal word but cannot understand the spiritual, symbolic meaning of what God is saying.

Acts 21:19-21 After greeting them, he related one by one the things that God had done among the Gentiles through his ministry. 20 And when they heard it, they glorified God. And they said to him, “You see, brother, how many thousands there are among the Jews of those who have believed; they are all zealous for the law, 21 and they have been told about you that you teach all the Jews who are among the Gentiles to forsake Moses, telling them not to circumcise their children or observe the customs.
COMMENTARY: It is believable that the Apostle Paul would tell converts not to circumcise children or observe other Jewish customs. He would do this because he understood the difference between the Old/First Covenant and New Covenant. He understood that circumcision of the flesh meant nothing to God.

Romans 4:1-11  What then shall we say about Abraham, our forefather according to the flesh? 2 For if Abraham was justified by works, he has something to boast about, but not before God.

3 For what does the scripture say? “Abraham believed God, and it was reckoned to him as righteousness.” 
COMMENTARY: Circumcision of the flesh is a religious law. People who follow religious laws do it with a sense of pride and boasting of how righteous they are because they follow religious laws. This is true for all religious people — including Jews and Christians.
Faithfulness to obey religious laws is honored only by people who follow those same religious laws. God is not at all impressed by obedience to religious laws. In fact, God calls obedience to religious laws sin.
The only obedience that God honors is with respect to his spiritual laws that are written on the heart. God credits righteousness only to people who believe him (i.e. hear and obey his spoken voice). Nothing else matters to God. All he really cares about is the condition of the heart.
4 Now to one who works, his wages are not reckoned as a gift but as his due. 5 And to one who does not work but trusts him who justifies the ungodly, his faith is reckoned as righteousness. 
COMMENTARY: People who serve God through religious works/activities believe that their works earn favor with God. Thus, whatever they might  receive from God, whether while they are physically alive or after they die, is considered to be a reward for doing the religious activity. If it is a reward for working, it is not a free gift.
This is a very different situation from the rewards that God gives to people who hear his spoken voice: The promised land.
6 So also David pronounces a blessing upon the man to whom God reckons righteousness apart from works: 7 “Blessed are those whose iniquities are forgiven, and whose sins are covered; blessed is the man against whom the Lord will not reckon his sin.” 9 Is this blessing pronounced only upon the circumcised, or also upon the uncircumcised? We say that faith was reckoned to Abraham as righteousness. 10 How then was it reckoned to him? Was it before or after he had been circumcised? It was not after, but before he was circumcised.
COMMENTARY: ***
11 He received circumcision as a sign or seal of the righteousness which he had by faith while he was still uncircumcised. The purpose was to make him the father of all who believe without being circumcised and who thus have righteousness reckoned to them,
COMMENTARY: The circumcision that Abraham received was of the heart — not of the flesh. That means it was a spiritual circumcision that was accomplished by God — not by man.
It is important to recognize that Abraham had faith before he was physically circumcised. As the scripture says, the reason it happened in this order is to make the point that righteousness is not dependent on physical circumcision. This also makes the point that righteousness is not dependent on baptism, communion, or any other religious ritual.
Titus 1:10-15 For there are many insubordinate men, empty talkers and deceivers, especially the circumcision party; 11 they must be silenced, since they are upsetting whole families by teaching for base gain what they have no right to teach. 12 One of themselves, a prophet of their own, said, “Cretans are always liars, evil beasts, lazy gluttons.” 13 This testimony is true. Therefore rebuke them sharply, that they may be sound in the faith, 14 instead of giving heed to Jewish myths or to commands of men who reject the truth. 15 To the pure all things are pure, but to the corrupt and unbelieving nothing is pure; their very minds and consciences are corrupted.

COMMENTARY: The circumcision party is a collective term that applies to anyone who adheres to and promotes religious laws. In the New Testament, it applied to religious Jews, but it now refers to all religious people. They are considered to be insubordinate men, empty talkers and deceivers. Such people are to be rebuked sharply so they might be turned from religion to faith.

Luke 2:21 And at the end of eight days, when he was circumcised, he was called Jesus, the name given by the angel before he was conceived in the womb.

COMMENTARY: Christians teach that Jesus was sinless. The fact that he was circumcised as an infant according to Jewish religious laws indicates that his parents sinned by having him circumcised.

The fact that Jesus spent some time in Egypt and was raised in the synagogue system symbolically represents that he was indoctrinated with religion. The fact that as an adult he willfully submitted to baptism also indicates that he participated in the sin of religion up to the moment before he was spiritually baptized by God. It was only after his spiritual baptism that it could be said that Jesus was sinless because all of his pre-baptism sins were forgiven according to the terms of the New Covenant.