The I Corinthians 7:18-20 passage cited in the previous post isn't primarily aimed at the physical act of circumcision--although one could possibly use that passage to describe the physical act of circumcision, but IMHO using this passage to do so is stretching that passage's context a bit.
The above cited passage's context actually begins back at I Corinthians 6:9 and extends to I Corinthians 7:20.
This portion of Paul's letter to the Corinthian church is an attempt to tell them what God expects His children to act in in several circumstances that arose in the Corinthian society.
The Corinthian society in which the local church was situated was perhaps one of the most morally corrupt ones of that day. Some commentators indicate that since Corinth was not only a seaport located in the small isthmus that connected the greater Macedonian area in the north to the southern Peloponnesian area. The principal reason why this city was a major trade route is because it provided a somewhat less dangerous path for ships to take than the often storm-filled central Mediterranean Sea route was during the oft unpredictable stormy season--see Acts 27 for a good example of the dangers that both ships & passengers had to contend while sailing on the central Mediterranean trade route.
Since Corinth was a very cosmopolitan city, it was also a city filled with idolatry and immorality--a common thing for many such global trading cities even today. Ships with peoples from not only the societies that immediately surrounded the quite extensive Mediterranean shore line (all of southern Europe & all of northern Africa), but also from various Black Sea and Asian & other African areas who had access to the Mediterranean via a canal that connected the Red Sea and the Lower Nile in Egypt.
With all this mixture of ideas from three continents, it's not hard to see that Corinth was quite a hodge-podge of lifestyles that expressed themselves in a variety of ungodly means. To be called a "Corinthian" in those days was about the worse epithet one could toss at his worse enemy!
This is why some commentators indicate the local church at Corinth was beset with perhaps more different kinds of problems than most of the other NT churches.
One common factor with any pagan religion down through the centuries is a perversion of God's standards of intimate relationships between men and women. One needs not examine too far into any pagan religion to notice that what possibly began with Lamech in Genesis 4:19 is still prevalent today in all pagan religions.
That being said, Paul answered the members of the local church at Corinth with HS-inspired advice that they need to be careful not to blend in with the world and accept its values and lifestyles--especially when it came to the subject of relationships between men and women.
The lifestyles of the Corinthians ran the gamut of those who thought that since our physical bodies are per se evil within themselves, they need to have as little contact with the opposite gender as possible--never marrying, or if one was married when he/she was saved, divorcing his/her spouse.
At the other end of the spectrum one found a fatalistic belief that since the physical body' urges can't be restrained at all, why not just live it up and enjoy all kinds of perverted intimacy from the other gender (or even within the same gender)?
Paul provides answers to these ideas:
1) While celibacy may be preferable in some circumstances, God nowhere demands that all men & women be celibate for their entire life. [It'd be kind of difficult for Adam & Eve to "fill the earth" if they were required to be celibate all their lives, wouldn't it?]
2) What if one marriage partner is saved & the other one isn't? That is not a legitimate reason to abandon the marriage partner.
3) While it's probably preferable to go into business with only Christians, that by itself isn't an all-encompassing command from God. If the occupation one has isn't expressly forbidden by God, this may give the Christian partner an opportunity to win that partner to Christ.
OTOH, Paul warns them to not fall trap of compromising Christian standards just to get along with one's business partner(s).
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These are the real reasons why Paul used the comparison of being circumcised or not being circumcised in I Corinthians 7:18-20.
