God has every right to treat us as mere creatures. Of course, such an action is absolutely unnecessary on God's part, and it is absolutely evidence of God's enormous love for us. Instead, God has made each person who trusts in Christ an heir to all the glories of God's kingdom along with God's only 'birth son' Jesus (John 3:16). Most of us would be satisfied to merely be saved from hell, to be given a quiet corner of heaven in which to spend eternity not suffering. In fact, Paul writes, our relationship to God is so far removed from that of slavery that we have become legal children with full rights as God's heirs. No, in His Spirit, Paul wrote in verse 15, God gave us the Spirit of adoption that enables to us to call Him 'Abba! Father!' He did not want to have a merely master/servant relationship with us.
Earlier, Paul wrote that though we exist to serve God, God has not given us the 'spirit of slavery' through His Spirit.
