What does Galatians 4:21 mean?

Paul's message to the Galatian Christians has been one of dismay. They accepted Paul's message of faith in Christ (Galatians 1:6), but then were deceived by false teachers claiming that they also needed to follow the law of Moses in order to be saved (Galatians 2:4). Paul made several appeals to change their minds, including a personal approach, seen in the most recent verses.

Here, Paul begins a new line of thought as he continues to explain why Christians should not add the works of the law to their faith in Christ in the hopes of being saved.

Paul is aware that other voices are arguing against him and the simple message of the gospel. After the Galatians had believed in Christ, a group of false teachers known as the Judaizers had arrived from Jerusalem to add to what Paul had taught. They apparently agreed that Gentiles (non-Jewish people) needed to believe in Christ, but they added on top of faith in Jesus the need to follow the law of Moses to be truly saved.

Paul wrote this letter because some of the Galatians, at least, were starting to believe the Judaizers. They were beginning to legalistically follow some parts of the law. In doing so, Paul has written, they were making themselves slaves again after Christ had made them free by their simple faith in the work He did in dying for their sins on the cross.

Now Paul asks his readers who seem to want to live under the law if they even know what it says. In other words, have they actually listened to the law for themselves or are they just listening to the teaching of the Judaizers?