Galatians 2:21

I do not set aside the grace of God, for if righteousness could be gained through the law, Christ died for nothing!"

(v21, NIV)

We have to remember that Paul is speaking to Jews. However, these aren't just Jews, but Jews who are now followers of Jesus. Since they were brought up as Jews, they have also brought in the culture and idea that you are justified by works. Following the law is how they were brought up and they feel it necessary for salvation. So, these Jewish Christians are the ones who Paul is directing or rather responding to. Paul continues to assert that it is not by following the law that we are justified, but it is by faith in Jesus that we are justified.

The real heart of the issue or lasting strike Paul delivers is this last point. If it is only through the law that we are justified, Jesus' sacrifice was for nothing. If all we have to do is follow the law, then we don't need Jesus. Therefore, his death on the cross meant nothing. If these Jews are in fact followers of Jesus, how can they follow Jesus if their actions leave no room for Jesus? It doesn't make sense. We are followers of Jesus and we should act as such. We need him and to live as if we don't proves that we are not his followers.