Galatians clearly shows Paul in his rhetorical flurry in correcting the fundamental error of the gospel that Peter had once preached. For Paul, one is reconciled to God solely through an act of grace on God’s part, the death of Christ. This act of God means that any attempt to impose any sort of Jewish legal regulation on Gentiles—especially circumcision—is a false gospel. This assertion by Paul is a startling shift from common Jewish (and Old Testament) belief that Gentiles need to be circumcised in order to claim to be part of the covenant.
Some of Paul’s harshest words in Galatians are reserved for those Jewish Christians in Galatia who were stirring up this trouble. Here, it is important to remember that Paul’s concern was not that Jews were undermining Christians. His concern was that ethnic Jews who were followers of Christ were upsetting the church from the inside. We should also remember that these Jewish Christians were not simply trying to make life difficult for Gentiles. They may have been reacting to external pressure from ethnic Jews who were accusing this new movement of being soft on Scripture (our Old Testament) and the entire Jewish tradition. Paul, in fact, was accused of peddling watered-down Jewish law to make “his gospel” more appealing to Gentiles.
Paul’s response to all this was to marginalize Israel’s law by claiming that it was merely a “tutor” or “custodian” until the gospel was revealed. And for those who continue to insist that circumcision is a necessary requirement for Gentiles, Paul simply directs to go all the way and emasculate themselves (5:12). What counts, Paul says, is not circumcision but a new creation. Within this context, this new creation really means participation in the new birth by means of Christ’s resurrection (6:16). This discussion is closely linked to Paul’s memorable description of the fruit of the Spirit: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control. There is no room for conceit, envy, and immorality among the people of God.
– Peter Enns