Some Galatians Backstory

The apostle Paul is probably the most famous missionary in history. After his conversion from Christian-bashing pharisee to Christian, he set out to plant churches all throughout the Roman Empire. Many of the books in the New Testament were written by him as letters to churches or individuals (Romans through Philemon). Galatians is considered to be one of the earliest of these letters and it deals a lot with the topic of "Legalism," even though that term is not specifically used. 

In the first century AD, the Christian movement was one that turned Judaism on its head. Paul and the other apostles likely did not see this as a new religion, but more a new era in Judaism. Jews in the first century had come to a place where the Law was paramount to any other issue. A look back at history showed a pattern of hard times following Israel's refusal to follow God's law, specifically in regards to circumcision, the sabbath and festivals, and food laws. The main opponents of Paul in Galatia are known as "Judaizers." They were Jewish Christians that criticized Paul for being to soft when it came to the law. Their message was one that, while Gentiles could be saved and Jesus' message applied to them as much as anyone, they must also adopt Jewish custom (food laws, circumcision, etc.) This message of rule following was obviously in contention with Paul's message of grace. This is why he wrote the letter. 

It would be easy to vilify these Judaizers for their convictions, but we need to keep a couple of things in mind.

• Jerusalem (and more specifically, the temple there) was the center of the Jewish religion. Faithful Jews would return for festivals annually (as Joseph and Mary did when Jesus stayed in the temple in Luke 2). Obviously, the farther away you got the harder that becomes and Jerusalem almost becomes a "once in a lifetime" trip for those Jews on the outskirts of Judea and Samaria.
• We call the Jews in the greater Roman Empire and outside of Judea and Samaria the "diaspora" Jews, or Jews of the dispersion. These would have been practicing Jews, but because they did not have access to the temple to make atonement sacrifices, they would have practiced an emphasis on following the Laws of the Old Testament to stay as pure as possible. 
• Christian converts (from JUDAISM) would likely have carried over some of these law-centric views, even after accepting Christ. 
• When Paul reached out to the Genitles (non Jews) in that area, he preached that the Spirit was the only thing that mattered, that we cannot live up to the law and so we must relish in the grace given by God. The Judaizers followed behind him and tried to add requirements of circumcision, etc. to these churches (see Gal 1:6-12). 
• Paul's emphasis in Gal 1:1-5, 11-12 on his calling and commission as an apostle (or in v.13-20, where he focuses on his track record and history) makes sense because he is trying to convince Judaizers that he is not watering down the gospel.
• He is also trying to convince the Galatians that he has the higher authority over those Judaizers trying to throw them into confusion. 
• It is VERY important to notice, finally, that the Judaizers were CHRISTIANS! They believed in Christ, but because of their world-view and past history, they did not fully preach an accurate message of Christ's sacrifice. We need to be careful of teachers like this. More importantly, we need to be careful that if we are claiming Christ's message of grace and love, we are not contradicting that message by being concerned with "doing enough to earn it."