Paul gets angry with the church because of their self efforts. He points out that they are justified by the spirit of God but are trying to work out their sanctification (perfecting) through their own willpower. This is a distortion of the gospel. We need to understand that everything we need for a life of holiness has already been given to us at salvation. It is through a greater revelation of Jesus that we are sanctified. Paul also shares that we are to receive a supply of the spirit which is his miracle power. In the example of Abraham and Sarah, the works of the flesh produced strife and suffering but the work of the spirit produced the fulfillment of the promise.