How do you obtain the power of the Holy Spirit for your life? Paul shifts focus to a second line of proof that the Christian life is lived by faith, and not by keeping laws. That line of proof is the Holy Spirit. How do you receive the Spirit of God, and all His miraculous blessings?
First: You receive the Holy Spirit by faith, not by keeping commandments (v. 2b). A good illustration of this is Cornelius, in Acts chapter 10. Cornelius was a Roman centurion. Although he apparently believed in the God revealed by the Old Testament, he was not yet a saved man. The Lord was drawing Cornelius, and as a result Cornelius was seeking God.
The Lord by means of a vision directed Peter to preach the Gospel to Cornelius and his family. Before Peter could even finish his testimony about Jesus Christ, the whole family received the Spirit of God, and gave evidence of it by praising God in miraculous tongues! Peter then had them all baptized. In this way Christian missions to the Gentile world began.
Cornelius didn't receive the Spirit of God by keeping a commandment. The Spirit of God came into Cornelius' heart because of his faith in the Gospel promise. Cornelius' example is God's rebuke to all those who preach that we must be water-baptized to be saved.
Second, what comes after receiving the Holy Spirit at salvation? Paul says that we continue the Christian life in the Spirit, the same way we started the Christian life in the Spirit -- by faith (v. 3). He says that people who say we have to switch over to law-keeping after conversion are foolish! Paul calls the Galatians "foolish" two times in just a few sentences. To say that we are obtain salvation by keeping a moral law, or that we retain our salvation by keeping a moral law, is the depth of foolishness. There is no good excuse for any sensible Christian to think this.
Why does God work miracles among us? Why does God supply the Spirit's power to a church? Paul says that miracles also come by faith, not by keeping Biblical laws (v. 5). Paul points to the miracle of Isaac's birth, recorded in the book of Genesis. Abraham was an old, old man, when God promised him and Sarah a son. How would it happen? Because Abraham kept a commandment? No! Because Abraham believed God, and God counted it to Abraham as righteousness (v. 6). God gave the circumcision commandment later, after He had already pledged His covenant with Abraham.
Has someone told you that you keep yourself saved by obeying the moral laws of the Bible? Don't listen to them. Paul says they are foolish. They show by such an idea that they do not understand the cross. Has someone told you that the Christian life is started by faith in the Gospel, and then lived by faith in the Gospel from beginning to end? That person is wise. The cross is not only how you begin the Christian life, it is your Christian life from beginning to end, and it is all a free gift!