According to Paul's teaching in Galatians, Christians become sons of God by

In the book of Galatians, Paul teaches that Christians become sons of God by having faith in Jesus Christ. He argues that it is not by observing the law or by any human effort that one can become a child of God. Instead, it is through faith in Jesus Christ that we are justified and become heirs of God's promise to Abraham. In Galatians 3:26-27, Paul writes: "For in Christ Jesus you are all sons of God, through faith. For as many of you as were baptized into Christ have put on Christ." Thus, it is through faith in Jesus Christ and being baptized into him that we become children of God.