"I am astonished that you are so quickly deserting the one who called you by the grace of Christ and are turning to a different Gospel - which is really no Gospel at all?"
What was this different Gospel that Paul was so irate about?
In essence it was that Jesus was a Jew and that while these religious Jews were believers in the resurrection of the dead (all Pharisees were) they didn't see how this changed their conception of Judaism; it was just one more bit of evidence that they were right. The way to please God was to obey the Law of Moses. So they were insisting that new converts to 'the Way' should obey the Law of Moses and the first thing was to get circumcised.
Circumcision preceded the Law of Moses. It was given by God to Abraham in Genesis 17. It was the sign of a new agreement or Covenant between God and him. Abraham's name was changed from Abram to Abraham (not just father, but father of many) and Sarai's name to Sarah. In this agreement God gave the land of Canaan as an everlasting possession to Abraham and his descendants, and promised to be their God. Circumcision was to be the sign of the Covenant.
Circumcision was an entry into the Passover feast (Exodus 13:48) and part of the Levitical Law (Leviticus 12:3), but the practice lapsed and those born in the desert after the exodus had not been cut, so Joshua had to circumcise the nation again (Joshua chapter 5).
However, quite early in its history the prophets of Israel recognized that circumcision could become just a token bit of holiness like wearing a crucifix or having a fish on your bumper. After the golden calf incident Moses told the Israelites, “Circumcise your hearts, therefore and do not be stiff-necked any longer.” (Deuteronomy 10:16) and this was picked up by Jeremiah preaching to the wayward Jerusalem and Judah, “Circumcise your hearts … or my wrath will break out and burn like fire because of the evil you have done.” (Jeremiah 4:4).
This same expression is taken up by Paul in his letter to the Romans. (2:28-29) “A man is not a Jew if he is only one outwardly, nor is circumcision merely outward and physical. No, a man is a Jew if he is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a man's praise is not from men, but from God.”
I guess that circumcision is not an issue with us today. In Africa, circumcision is recommended because it reduces the incidence of sexually transmitted disease. Researchers from Johns Hopkins University, found circumcision reduced the risk of herpes by 25%, and human papillomavirus (HPV) by a third. Three randomized trials in Africa have demonstrated the protective effects of male circumcision on HIV infection (transmission of HIV is reduced by as much as 60%) and Uganda has recently announced attempts to increase male circumcision.
In recent decades, most medical organisations in the west have deemed the practice not medically necessary, except in rare cases. The American Academy of Pediatrics has established a taskforce to examine its policy on circumcision and a similar investigation is underway in Australia but in the UK no review is planned. Why? The procedure is much more popular in the USA than the UK—65% of US men are circumcised (though it is much rarer in Blacks and Hispanics) versus 16% in the UK. In general in the UK it is regarded as an intrusive assault that is unnecessary.
So we shouldn’t use Galatians to justify or nullify a minor medical operation. Paul’s objection is not to the medical practice but to what is in the heart, and what that is about we shall see later.