How according to Paul could a Christian rightly become a child of God?

According to Paul in his epistle to the Galatians, he stressed that man was a slave under the law, but was redeemed through faith in Jesus Christ. With the coming of the son of God – Jesus Christ, our faith in him has made us children of God. Through our baptism in Christ, we have put on Christ. Therefore, Jesus is already in us. Because of this, there is no distinction of race or sex. If we are Christ’s children, then we are Abraham’s offspring by faith, hence heirs of God’s promise. We can not be fully matured if we remain like children in our faith. We were subject to the elemental spirits of the universe, but God in His infinite mercy sent His only son to redeem those under the law and to adopt us as sons. We can then call God our father as adopted sons. So, through Jesus, we are no longer slaves, but sons and rightful heirs of eternal life.
There are so many ways to show that we are children of God. These include:
(i) We should reject Satan in every sphere of our lives and accept Christ as our saviour.
(ii) We must obey and fulfil Christian obligations and those of state also.
(iii) We must strive hard to win more souls for Christ and contribute our quota in cash and kind towards the propagation of Christianity.