Galatians 3-4

Paul gets into full swing in his argument here.  His main point is to sway the Galatian believers back away from following the false teaching of the "circumcision group" who says that to be a true Christian, you must be circumcised (5:2), follow the Jewish holidays (4:10) and follow the rest of the law of Moses.
Paul is saying that they began with the Spirit (3:3), that is by believing what they heard and trusting Christ Jesus for salvation (v2), that they are now being led astray to think that human effort is required to make them "true Christians".

He says that the Law of Moses was like guardian or a schoolmaster that was put in place to guide and supervise people while they were still young (3:25).  But then we were set free once faith came and that now we are heirs and not servants or schoolchildren (3:29).

Another point of interest that is harder to see in the NIV is the term "basic principles of the world" (4:3) and "weak and miserable principles" (4:9).  These terms actually refer to what spiritual powers would have previously held these gentile believers captive.  When read in that light, terms like "slavery" (4:3,9) make sense in a slightly different way.

The final point that I found quite interesting is Paul's description of Hagar versus Sarah and physical Jerusalem versus spiritual Jerusalem.  This Jerusalem that is "above" reminds me of Revelation 12:1, the picture of spiritual Israel or Jerusalem.

The key points here are not to be pulled into a belief that we can/need to earn our way into a relationship with Christ by bein perfect or following all the rules.  In chapter 5 Paul comes full circle and describes how we must not use the freedom that we have to sin but that we must still obey the law of Christ.  This is crucially important to understand this distinction because this really gives the foundation for how a Christian is to relate to the law of the Old Testament - what applies and what doesn't.  More on that later :).