For an introduction to this series, click here.
Paul has a very important question to ask in this chapter:
"O foolish Galatians! Who has bewitched you? It was before your eyes that Jesus Christ was publicly portrayed as crucified. Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith? Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh?" (3:1-3)
Paul does not even provide an answer to this question, because it is so obvious. This is the critical question of the book, and it blows the lid off of legalism. I have heard lots of legalists defend their false teaching by saying that they are not saying you need to follow their rules in order to be saved, but they say these rules are for Christian living. Paul says here that definition is too narrow. Yes, adding man's works to salvation is certainly legalism. But Paul points out that sanctification is just as much a part of salvation as justification. The legalists say that yes, the Lord is able to bring a lost person to justification, but the Lord needs some help in sanctifying that person. He needs my rules to help the young Christian live the life. Now of course there are some obvious rules for Christian living in the Bible that are not negotiable. But to tell a Christian that they are not right with God if they don't do exactly what you do is just as much a sin as it is to tell someone they need to do some penance each day in order to go to heaven.
The rest of the chapter tells us about the example of Abraham, and how we are justified as Abraham was: by faith.
"Does he who supplies the Spirit to you and works miracles among you do so by works of the law, or by hearing with faith— just as Abraham 'believed God, and it was counted to him as righteousness'? Know then that it is those of faith who are the sons of Abraham. And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, 'In you shall all the nations be blessed.' So then, those who are of faith are blessed along with Abraham, the man of faith." (3:5-9)
"Christ redeemed us from the curse of the law by becoming a curse for us— for it is written, 'Cursed is everyone who is hanged on a tree'— so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit through faith." (3:13-14)
Paul explained that Moses' law put people under a curse, since no one could perfectly keep it. Christ's death took away that penalty. Paul explains the purpose of the law:
"Is the law then contrary to the promises of God? Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law. But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe. Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. So then, the law was our guardian until Christ came, in order that we might be justified by faith. But now that faith has come, we are no longer under a guardian, for in Christ Jesus you are all sons of God, through faith. For as many of you as were baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. And if you are Christ's, then you are Abraham's offspring, heirs according to promise." (3:21-29, ESV)
The purpose of the law was to act as a guardian or baby sitter until the more perfect way of faith was revealed. Certainly the law was spiritual - read the Psalms if you doubt that - but salvation has always been through faith.
Now the passage about Jew/Greek, slave/free and male/female is an important passage for us to understand. Feminist theologians (yes, they are out there, and it is a growing movement) use this passage to point out that Paul is teaching here that there are no different roles for males and females in the church. They would be those who would discount the "husband of one wife" requirement for pastors as either sexist or not really written by Paul and therefore not as authoritative. If you read this in context, Paul is comparing the male/female to the Jew/Greek relationship, saying that just as God views males and females as equal, He views Jews and Greeks as equals.
Critics of Paul (I don't know how you can claim to be a Christian and be a critic of Paul, but nevertheless) say this passage and a few others prove that Paul approved slavery. Paul's epistles have to be interpreted in the political context in which they were written. Rome was the ultimate authority. If Paul had written his epistles in say, early 19th century America, I think Paul would have been supportive of those who were trying to abolish slavery. But Paul saw that Christianity is not a movement for political change, but instead is a simple, everyday life. And if that means living in a world where there is slavery, we need to make the best of it.