Galatians 4:6-7

All who put their faith in the saving work of Jesus on the cross receive grace enough to become the children of God. The words used in scripture to describe this reality show the inability of man and the power of God in this relationship – salvation, redemption, reconciliation, adoption. These are all things that a person has done to them by God, not something that a person can do to themselves. In Galatians 4, Paul uses the imagery of adoption to explain the truths of being forgiven and accepted by God.
Having been forgiven of our sins and received by God, Paul says that we have “received the adoption of sons.” As the children of God, however, we do not continue to live in sin as if nothing has changed. Rather, we have received a new nature. In verse 6, Paul explains that God has sent the Holy Spirit to live inside of those who believe. This indwelling Spirit serves to strengthen believers in time of need, to convict believers in time of sin, and to quicken believers to obey God, their Father.
The Judaizers had come to Galatia and told the believers that in order for God to be pleased with them and for them to be saved, they must put their faith in Christ and obey the law of Moses. Paul explains that this simply is not the case. He compares someone who is working to obey the Law for the approval of God to a slave or a “servant.” They see God as a Master, who they in fear and oppression must appease by following every nook and cranny of idiosyncrasy in the law. Like timid slaves, they constantly hover at the edges of obedience always fearful that the Master will see their ineptitude and execute judgment and wrath against them.
Paul explains that when a believer is converted, the Spirit of God comes and dwells inside of him. The Galatians who had put their faith in Christ were not left as slaves under the oppressive thumb of a domineering task-master. Rather, they were indwelt by the Holy Spirit and had become sons to God. Their relationship with Him was intimate and because He had saved them, and because He had demonstrated His love for them, as sons they sought to obey and fulfill his every desire and command. The motivation was strikingly different between sons and slaves.
We too can come to God understanding that He is not in fact a Cosmic Killjoy with a billy-club poised to crush our skull at the first inkling of disobedience. Rather, He is a loving Father who has already extended saving grace to those who are His own, and as a Father, He continually shows grace to those who are His sons and daughters. Now, because of His love that He has for us, we can obey, not out of fear or terror, but out of an obedient heart of love for the Father.

Food For Thought: Explain the difference of motive in obedience between a servant and a son.