Empowered Initially and Continually by the Spirit

Galatians 3:2   Let me ask you this one question: Did you receive the Holy Spirit by obeying the law of Moses? Of course not! You received the Spirit because you believed the message you heard about Christ. 

Paul has confronted Peter and the Judaizers about following another gospel.  Here Paul is giving a characteristic of a false gospel as compared to the true gospel.  He points out to them that truly following the gospel is being empowered by the Holy Spirit which was given to them because they believed the message of Christ.  Walking with God is a continuing to walk in belief which gives the Holy Spirit control in our lives.  

Paul is using questions here to break down the false message and point the people back to the core message of the gospel.  The core message is belief in the testimony of Christ which results in life (Spirit guided life).